Resumos

Transcrição

Resumos - Universidade Federal do Ceará

XIV Escola Brasileira de Estrutura Eletrônica
1
A study of SiH+ molecule and its isotopômero SiD+
Felipe Oliveira Ventura, Cristina Porto Gonçalves
Universidade Estadual do Sudoeste da Bahia - UESB
In this paper a theoretical study of the SiH + molecule and its isotopômero SiD+ , where D is deuterium appears. Ion Silylidyne, SiH + , is a molecule of astrophysical interest first observed experimentally in studies of laser
spectroscopy with production of photodissociation [1] spectrum, and then detected in the photosphere of the Sun
[2]. This molecule has been studied both experimentally and ab initio, because it is expected to be even found
in interstellar regions of star formation due to high occurrence of photoionization and photofragmentation of molecules in this region. Previous studies of photodissociation, Feshbach resonance and electronic structure can be
found in the literature [3,4,5]. In this work the potential energy curve (PEC) were studied, the dipole moment,
the ionization potential (IP) , the dissociation energy (Do ) and electron affinity (EA) of SiH + and SiD+ . The
calculated electronic energies occurred at the level of the Born- Oppenheimer approximation (ABO) and the level of
correction Finite Nuclear Mass (FNMC - Finite Nuclear Mass Correction). The FNMC is a methodology proposed
by J.R. Mohallem and colleagues [6] that goes beyond the Born-Oppenheimer approximation and allows the study
of isotopic effects on the level of molecular electronic systems without the need to work with the nuclear level, and
predicts ABO to separate the electronic movement of nuclear movement. The computer package used in the study
was the GAMESS with FNMC inclusion of the source code of software. The Density Functional Theory (DFT) was
used with the B3LYP functional and cc-pVQZ basis. The interatomic distances to obtain the CEP and the dipole
moment understood the regions away from equilibrium (2.858 bohrs) and molecular dissociation. The values were
compared with experimental data and literature data and proved satisfactory.
Thanks: To the State University of Southwest Bahia through the support of Dean of Research and Graduate
Studies - PPG.
[1] A. E. Douglas and B.L. Lutz, Can. J. Phys. 48, 247 (1970). [2] N. Grevesse and A. J. Sauval. Astron.
Astrophys., 9, 232 (1970). [3] P. C. Stancil et al. Astrophys. J., 486, 574 (1997). [4] P. J. Sarre et al. Phil. Trans.
R. Soc. Lond. A. 324, 233 (1988). [5] J. M. O. Matos et al. J. Chem. Phys. 89, 423 (1988). [6] J. R. Mohallem,
F. Rolim e C. P. Gonçalves, Mol. Phys. 99, 87 (2001).
2
A study of electron correlation on the BH molecule and its isotopômero BD by first-principles
methods
Felipe Oliveira Ventura, Cristina Porto Gonçalves
Universidade Estadual do Sudoeste da Bahia - UESB
In this paper a theoretical study of BH (boranylidene) molecule and its isotopômero BD, where D is deuterium
appears. The objective of this study was to investigate the influence of electron correlation in the description of
electronic properties of BH and its isotopic species, the BD. It is of fundamental importance for the calculation of
molecular properties data that take into account the effects of electron correlation, so that these properties can be
described with good accuracy, explaining the experimental data. In this work the interaction Settings (CISD), Perturbation Theory of Möller-Plesset (MP2) and Density Functional Theory (DFT) methods with B3LYP functional
were used in obtaining the potential energy curve (PEC), the dipole moment , dissociation energy (Do ), ionization
potential (IP) and electron affinity (EA) of BH and BD, respectively. The data were compared with the HartreeFock method (HF), by using this just a Slater determinant and not describe the effect of electron correlation,
and then comparing the methods themselves. ADZP the basis set and AQZP (http://www.cce.ufes.br/qcgv/pub/)
were used in the description of BH and BD, respectively, with the computer package GAMESS. The interatomic
distances to obtain the CEP and the dipole moment understood the regions away from equilibrium (1.2248 angstroms) and molecular dissociation. Particularly for the study of BD isotopômero, Correction Finite Nuclear Mass
(FNMC) proposed by JR Mohallem and colleagues [1], which allows the study of isotopic effects already at the
level of molecular electronic systems without the need to work with was used The nuclear level. The results were
compared with data in the literature [2,3] and experimental data and proved satisfactory. Among the methods
showed the best result for the molecular properties of the DFT/B3LYP was raised, along with AQZP basis.
Thanks: To the State University of Southwest Bahia through the support of Dean of Research and Graduate
Studies - PPG.
[1] J. R. Mohallem, F. Rolim e C. P. Gonçalves, Mol. Phys. 99, 87 (2001). [2] A. Dutta and C. D. Sherrill, J.
Chem. Phys. 118, 1610 (2003). [3] M. Jaszuski, B. O. Roos, and P. Widmark, J. Chem. Phys. 75, 306 (1981).
3
Optical properties of β-Ga2O3 nanowires grown by two MOCVD/CVD techniques
Marco Sacilotti
UFPE-DF-Recife
Ronaldo de Melo, Cid Araujo, Anderson Gomes, Remi Chassagnon, Eduardo Falcao, SeverinoA. Jr
DF-UFPE-Recife Br& Univ. Bourgogne Fr
We propose a new and simple two combined CVD routes to produce gallium oxide nanowires. Beta-gallium oxide
is a versatile oxide wide band gap material (from 4.4 up to 5.68 eV), which exhibits particular electrical conduction
and optical properties. It is a material for several technological applications as optoelectronic nanodevices. Large
surface area/volume ratio of nanowire presentation can increase these properties. This work presents a very simple
route to obtain β-Ga2O3 nanowires. First, metallic perfect gallium structured spheres (micrometer and nanometer
sized) were grown on cleaned (100) Si substrates in a MOCVD system, using trimethylgallium (TMGa) as Ga
source. The distribution of these Ga spheres is quite uniform and dense on the Si surface. Following this step, the
gallium spheres, obtained by MOCVD, were thermally annealed at 700-900 o C (760 torr) in a linear CVD furnace
under pure oxygen atmosphere from 15 up to 120 minutes. The gallium sphere/gallium oxide nanowires, after the
oxidation process, looks like sea urchin animals. Dense β-Ga2O3 nanowires were obtained on silicon substrate by
this new route. SEM shows tens of micrometer long nanowires (with 20-40 nm diameter) gallium oxide, grown
from the gallium spheres surface. The growth procedure comes from the gallium sphere surface, contrary to the
VLS growth technique (with the growth being on the top of the nanowire). SEM revealed that these nanowires
are dense and continuous on the Ga spheres surfaces. EDS confirmed that the nanowires present only Ga and O
and TEM confirms the crystalline structure of the
beta -Ga2O3 nanowires. 300 to 10 k luminescence indicates three mains emission regions: UV-blue, green and red
regions. Most of the emission peaks are newly regarded as interface quantum states emission, from two different
materials phases: a core/shell structure composed by β-Ga2O3/a-Ga2O3. To the β-Ga2O3 crystalline bulk phase it
is included an a-Ga2O3 nanoclusters amorphous phase. Our model explain most of the electrical/optical properties
of gallium oxide familly, not understood up to now (e.g.: its bandgap uncertainty). The electronic structure of the
core/shell system being more important than the bulk crystalline structure. The obtained sea urchin-like structures
were used as scattering medium to produce room temperature random laser-like action in the 560- 580 nm optical
band using Rhodamine 6G (Rh6G)/PVA as the gain medium.
4
Magnetic Fied Induced Vortices in Graphene Quantum Dots
Ícaro R. Lavor, D. R. da Costa, A. Chaves, G. A. de Farias.
Departamento de Fı́sica, Universidade Federal do Ceará, Fortaleza, Ceará, Brasil.
R. Macêdo
School of Physics and Astronomy, Kelvin Building, University of Glasgow, Glasgow, G12 8QQ United Kingdom.
F. M. Peeters
Departament of Physics. University of Antwerp, Groenenborgerlaan, Antwerp, Belgium.
The vortex formation in the Cooper pairs density of superconductors in the presence of an external magnetic field
has been widely studied for many years. In a recent paper, magnetic field induced vortices were observed also in the
eigenstates of semiconductor quantum dots (QD) with square and triangular geometries, where electron obey the
Schrodinger equation within the effective mass approximation. On the other hand, graphene, one of the crystalline
forms of carbon, isolated for the first time in 2004 by micromechanical cleavage of graphite, exhibits an almost linear
energy dispersion, so that low energy electrons in this system rather obey the Dirac equation for massless fermions.
Furthermore, graphene has quite peculiar properties, as for example, its high electrical conductivity, making it
a highly strategic material for the development of electronics devices. Therefore, understanding the behavior of
electrons in graphene under applied fields is of great important for the development of new technologies. In this
sense, a more fundamental question rises: would electronic states of a graphene QD exhibit magnetic field induced
vortices, as those observed for semiconductor QD?
In this work, we investigate the local current density pattern of the eigenstates of graphene QD under a
perpendicularly applied magnetic field, by diagonalizing the tight-binding Hamiltonian. Our results demonstrate
that, as the magnetic field intensity increases, vortices and anti-vortices appear in the local current density of the
quantum dots for specific configurations of the system, such as zigzag triangular dots and squared dots defined by a
mass term. The increasing number of vortices in a given eigenstates is reflected into the crossings and anti-crossings
observed in the energy spectra of these systems.
5
√
√
Study of doped B/Si(111)( 3 × 3)R30◦ defects using ab initio total energy calculations
D. P. de Andrade, R. H. Miwa
Instituto de Fı́sica, Universidade Federal de Uberlândia, CP 593, 38400-902, Uberlândia, MG, Brazil
A. B. McLean
Astronomy, Queens University, Kingston, Ontario, K7L 3N6 Canada
It is well know that B atoms easily diffuse in Si bulk crystal at high temperatures√owing
√ to their small
√ atomic
radius[1]. In this context, we have studied near surface defects the doped B/Si(111)( 3 × 3)R30◦ (B 3) system
using ab initio total energy calculations. We provide a B/Si(111) map of energetic
stability and electronic properties.
√
Initially we examine the equilibrium geometry, and the properties of the B 3 pristine surface. The B atom occupies
the subsurface site underneath the topmost Si adatom, giving rise to a B δ-doped layer. The electronic band
structure and the calculated projected density of states (PDOS) confirms
√ the semiconducting character of the
surface. Next, we examine the energetic stability of several defects in B 3. The dangling bonds defects leads the
bright feature in the empty state image and this has been identified to as Si atom in the S5 substitutional site
(Si-S5) located below the Si adatom [2]. Changes in the surface electronic charge density were examined through
STM √
simulations and compared with the experimental STM pictures [3-4]. We observed the electronic structure of
the B 3 defects surface is modified by changing the positions of the B atoms. We also calculate STM images, as
well as the energetic stability, for several structures with an additional substitutional B dopant
√ (new configurations)
placed in different subsurface sites to understand influence of the extra B atom on the B 3.
[1] H. Hirayama, T. Tatsumi, M. Abe, P. Jelinek, R. Perez, S. Morita anda O. Custance, Nature 446, 64 (2007).
[2] H. Q. Shi, M. W. Radny, and P. V. Smith, Phys. Rev. B 66, 085329 (2002).
[3] M. Berthe, A. Urbieta, L. Perdigão, B. Grandidier, D. Deresmes, C Delerue, D. Stiévenard, R. Rurali, N.
Lorente, L. Magaud, an P. Ordejón, Phys. Rev. Lett. 97, 206801 (2006).
[4] C. Tournier-Colletta, B. Kierren, Y. Fagot-Revurat, and D. Malterre, Phys. Rev. B 87, 075427 (2013).
6
Interaction between a carbon nanowire and nanotubes flattened
Aliliane Almeida, Sergio Azevedo
Departamento de Fı́sica, CCEN, Universidade Federal da Paraı́ba, Caixa Postal 5008, 58051-900 João Pessoa - PB, Brazil
We investigated the effect of the radial compression on the electronic structure of BN and Carbon nanotubes
interacting with a carbon nanowire. It is shown that the electronic properties of BN nanotubes under compression
are strongly dependent on the direction of the BN and carbon stripes parallel or perpendicular to the tube axis.
For perpendicular configurations there are remarkable reductions of the gap energy. The magnitude of the gap
reduction with compression is intermediate between those of carbon and boron nitride nanotubes. It is found
that the reduction of the energy gap is associated to C-N pairs located at the curved region of the flattened
tube. However, when the C stripes are parallel to the tube axis the structures it is found a different behavior.
For model-III structures the radial compression induces the opening of an energy gap of about 0.83 eV, which is
independent from the flattening ratio. For model-IV nanotubes it is found that the electronic properties remain
basically unaffected by the radial deformation, presenting a metallic behavior for all values of Z. Concerning Cdoped tubes it is observed that the energy states associated to the conduction band decreases with the flattening
ratio, leading to a significant reduction in the gap energy. For the special case of CN-I structures the C impurity
introduces an empty localized energy level close to the valence band. Therefore, due to the fact that the electronic
states associated to the valence band are not affected by the radial deformation, the gap energy is not modified.
[1] J.R. Martins, H. Chacham, ACS Nano 5 (2011) 385.
[2] X. Blase, J.C. Charlier, A.D. Vita, R. Car, Appl. Phys. A 68 (1999) 293.
7
Vibrational spectra and DFT calculations of sonderianin diterpene
B.G. Cruz, A.M.R. Teixeira, I.M.M. Oliveira, D.M. Sena Junior
Universidade Regional do Cariri
H.S. Santos, J.W. Sousa, P.N. Bandeira, M.R.J.R. Albuquerque
Universidade Estadual Vale do Acaraú
P.T.C. Freire
Universidade Federal do Ceará
G.O.M. Gusmão
Universidade Estadual do Piauı́
Croton is an extensive genus comprising around 1.300 species from Euphorbiaceae family. One of these species
is Croton blanchetianus, restricted Brazilian semi-arid region, known popularly as marmereiro-preto. The ethno
pharmacological information refers to this plant as having anti-inflammatory and gastro protective properties [1].
The sonderianin diterpene (C21 H26 O5 ) was isolated from the stems of Croton blanchetianus and its structure
was elucidated by Nuclear Magnetic Resonance (NMR) and by X-ray crystallographic analysis [2]. The crystal
of sonderianin at room temperature belongs to orthorhombic structure with space group P21 21 21 and lattice
parameters: a= 7.314 Å, b=10.481 Å, c=24.276 Å [2]. Having found no pertinent vibrational spectroscopy study in
the literature, here we report a study of the characterization of sonderianin diterpene crystals by means of Fourier
Transform infrared attenuated total reflectance (FTIR-ATR) and Raman spectroscopies. In addition, Density
Functional Theory (DFT) calculations were performed with the objective of gaining insight about the normal
modes of this diterpene. The FTIR-ATR and Raman spectra of the crystal were recorded at room temperature in
the regions 600 cm−1 to 4000 cm−1 and 50 cm−1 to 4000 cm−1 , respectively. Calculations using DFT were carried
out using the Gaussian03 package. Vibrational wavenumber and wave vector have been predicted using DFT
calculations with Lee-Yang-Parr correlation functional (B3LYP) and the basis set 6-31 G(d,p). The description of
the normal modes of vibration was carried out based on the visualization of the atomic displacement representations
for each vibration, using the Chemcraft program. The calculated spectra were adjusted to experimental data by a
scale factor of 0.9612 reproducing the experiments with good agreement. This agreement allowed us to assign the
normal modes present in the FTIR-ATR and Raman spectra of sonderianin diterpene crystal.
References:
[1] Amaral, J. F. Dissertação (Mestrado) - Universidade Federal do Ceará - Pós-Graduação em Farmacologia,
Fortaleza, 2004.
[2] Craveiro, A. A. et al. Phytochemistry, 20(4), 852-854, 1981.
8
ELECTRONIC AND SPECTROSCOPIC PROPERTIES OF DOPED GRAPHENE FLAKES
Damon Ferreira Farias, Roberto Rivelino
Universidade Federal da Bahia-UFBA
Due to its unique properties, graphene has been the subject of intense research for decades. Nowadays, advances in
graphene-based systems have demonstrated that graphene continues to be the ideal candidate for the application
in low-dimensional electronics, material sciences and nanotechnology. Recently, fabrication methods of producing
large and flat graphene flakes have opened new perspectives for the graphenes research. As a complementary
technique accompanying its fabrication, spatially resolved Raman spectroscopy is commonly employed to assess
the occurrence of single layered graphene flakes. Interestingly, in order to deal with these nanoflakes, its oxidized
form (graphene oxide) is largely preferred, since the hydroxyl functional groups enable it to be stably dispersed in
water and chemically modified. In this work, we have employed density functional theory methods to investigate
electronic and Raman scattering properties of small graphene-like pieces [1]. Our calculations were performed
within the hybrid B3LYP functional scheme combined with the 6-311+G(d,p) basis set. First, all the considered
graphene-like structures were fully optimized to obtain their Raman spectra and related light scattering properties.
Second, a systematic and comparative electronic structure analysis of the nanoflakes was performed to investigate
the size effects on the studied properties. Finally, we have investigated the properties of some oxidized forms of
these graphene-like pieces as starting point to obtain other stable doped systems [2,3] with interest for application
in nanoelectronics. Financial support: CNPq, CAPES and FAPESB. Computational facilities: CENAPAD-SP.
[1] R. Rivelino, R. B. dos Santos, F. de B. Mota, G. K. Gueorguiev, J. Phys. Chem. C 114, 16367 (2010).
[2] R. B. dos Santos, R. Rivelino, F. de B. Mota, G. K. Gueorguiev, Phys. Rev. B 84, 075417 (2011).
[3] R. B. dos Santos, R. Rivelino, F. de B. Mota, G. K. Gueorguiev, J. Phys. Chem. A 116, 9080 (2012).
9
Ab initio study of graphene with functionalizations
Mariana Zancan Tonel, Ivana Zanella, Solange Binotto Fagan
Centro Universitário Franciscano
Graphene has attracted great interest from the scientific community since their stability was shown in 2004 [1].
This nanomaterial has a range of applications ranging from electronics to biomedicine, which is justified by its
characteristics, among them we can mention: two-dimensional planar geometry, high electron mobility and quasirelativistic dynamics of electrons [2]. However, its structure makes it highly hydrophobic nanomaterial which
hinders its application in this environment. And one of the ways to change this feature is by adding functionalization
with carboxylic groups, hydroxylic and/or carbonyl groups in its structure [3,4]. Therefore in this work aims at
studying the properties and electronic through the computer code SIESTA isolation of graphene functionalized
with carboxyl, hydroxyl and carbonyl. Preliminary results show that addition of a carboxyl group in the structure
causes a graphene near the Fermi level and in this case the binding energy level is -1.10 eV.
[1] NOVOSELOV, K. S. et al. Electric Field Effect in Atomically Thin Carbon Films. Science, v. 306, p.
666-669, 2004.
[2] GEIM, A. K.; NOVOSELOV, K. S. The rise of graphene. Nature Materials v. 6, p.183 - 191, 2007.
[3] YANG, F.O. et al. Chemical Functionalization of Graphene Nanoribbons by Carboxyl Groups on StoneWales Defects. J. Phys. Chem. C, v.112, p. 12003-12007, 2008.
[4] KUILA, T. et al. Chemical functionalization of graphene and its applications. Progress in Materials
Science, v. 57, p.1061-1105, 2012.
10
Ab initio study of graphene and its derivatives interacting with dopamine
Mariana Zancan Tonel, Solange Binotto Fagan
Graphene has attracted great interest from the scientific community since been demonstrated its stability in 2004
[1]. Due to its structural and electronic characteristics, has potential for a wide range of applications, from the
electronics industry to medicine. Graphene is a single layer of graphite in which carbon atoms are arranged in
hexagonal form. Meanwhile dopamine (DA) is an important neurotransmitter from the central nervous system of
mammals. At low levels the DA may lead to neurological disorders such as Parkinson’s disease and schizophrenia
[2]. Experimental studies show that graphene based systems would be effective in the detection of dopamine,
which would be interesting for the development of sensors for the quantification of neurotransmitter can aid in the
diagnosis and treatment of various diseases [3].
The objective of this study is to evaluate by computational ab initio simulations, the electronic and structural
properties of pristine graphene and functionalized with carboxyl, carbonyl and hydroxyl groups interacting with
the DA molecule making use of the computer code SIESTA [4]. Preliminary results show that the interaction
between graphene and its derivatives with dopamine is low in the order of -0.38eV, without change in the electronic
structure.
[1] NOVOSELOV, K. S.; GEIM, A. K. ; MOROZOV, S. V. et. al. Electric Field Effect in Atomically Thin
Carbon Films. Science, v.306, p. 666-669, 2004.
[2] KIM, J. et al. Dopamine neurons derived from embryonic stem cells function in an animal model of Parkinson’s disease. Nature, v. 418, p. 50-56, 2002.
[3] LIU, S.; SUN, W.; HU, F. Graphenenano sheet-fabricated electrochemical sensor for the determination of
dopamine in the presence of ascorbic acid using cetyltrimethylammonium bromide as the discriminating agent.
Sensors and Actuators B: Chemical, v.173, p. 497-504, 2012.
[4] SOLER, J. M. et al. The SIESTA method for ab-initio order-N materials simulation. J. Phys.: Condens
Matter v.14, n.11, p. 2745-2779, 2002.
11
TEMOZOLOMIDE AND FULLERENES MOLECULES INTERACTING VIA MOLECULAR
MODELLING
Laura F. O.Vendrame, Solange Fagan, Ivana Zanella
Due to their interesting physical and chemical properties, fullerenes have great importance in nanoscience and
nanotechnology nowadays. The use of such nanometric systems, functionalized or in pristine form, as chemical
and biological sensors has become a large field of study and application [1]. Just the C60 acting with drugs
already encompasses a large field of study and has improved many studies, specially those drugs pertaining to
fight cancer, as well as those with controlled drug delivery [2]. One of the purposes is that the release and
stability of the active principle may be controlled, with the possibility to deliver the drug to a specific organ [4],
avoiding undesirable effects. The purpose of this work is to evaluate the structural and electronic properties of
various configurations of the temozolamide molecule interacting with functionalized fullerenes. This drug is very
important to medicine for the treatment of brain tumors and its also indicated for the treatment of patient with
metastatic malignant melanoma in advanced stage [3]. The interaction of the temozolamide drug with pristine
and functionalized fullerenes is important for the future developing of central nervous nanodrugs systems that
addresses the performance and increase the specificity of the drug deliver, improving its permeability and reducing
its neurotoxicity. In this work, are investigated through ab initio calculations structural and electronic properties
of these fullerenes, in carboxylated forms, interacting with temozolamide molecule in various configurations. The
obtained results demonstrated that the temozolamide molecule presents interaction when adsorbed on the fullerenes
with binding energy between 0.28 eV and 0.54 eV. The adsorption occurs via physical regime showing irrelevant
changes in the electronic structure. This result are of a great interest for the use of the fullerene as a drug carrier.
K. Work: Ab Initio, Fullerene, Temozolamide.
REFERENCES
[1]GROBMYERA R. S., KRISHNAB V., Minimally invasive cancer therapy using polyhydroxy fullerenes.
European Journal of Radiology, v.81 p.51-S53, 2012
[2] PAWEL M. et al., Functionalized fullerenes mediate photodynamic killing of cancer cells: type I versus type
II photochemical mechanism. Free Radical Biology Medicine, v. 43 p. 711-719, 2007.
[3]PETRELLA T. et al., Single-agent interleukin-2 in the treatment of metastatic melanoma: A systematic
review. Cancer Treatment Reviews, v.33, p.484-496, 2007.
[4]ZANELLA, I; et al., Ab initio study of pristine and Si-doped capped carbon nanotubes interacting with
nimesulide molecules. Chemical PhyscsLetters, v. 439, p. 348 -353, 2007
12
Encapsulamento de fios metálicos em nanotubos de carbono deformados
W. S. Melo, Eduardo M. Diniz, S. Guerini
Universidade Federal do Maranhão
Os nanotubos de carbono descobertos em 1991 por S. Iijima [1] possuem propriedades fı́sicas e quı́micas muito
interessantes, além de possibilitar um ambiente favorável para a formação e crescimento de nanofios metálicos, uma
vez que estes são instáveis na forma livre [2]. Neste trabalho estudamos as propriedades estruturais, eletrônicas
e magnéticas de fios lineares de ferro encapsulados por nanotubos de carbono achatados com e sem hidrogênios
ligados aos átomos de carbono das extremidades laterais. Também realizamos cálculos em nanofitas de carbono com
nanofios de Fe intercalados. Para investigar essas propriedades utilizamos cálculos de primeiros princı́pios baseados
na teoria do funcional da densidade, implementados no código computacional SIESTA [3]. Nossos resultados
mostraram que o tubo achatado com o nanofio encapsulado é estável e esta estabilidade deve-se às interações entre
os átomos metálicos e os átomos de carbono. Observou-se também, que devido ao achatamento os átomos do fio
ficam desalinhados e a dimerização do nanofio não provoca alterações consideráveis nas distâncias entre um átomo
e seus vizinhos. Além disso, verificou-se que energeticamente nanofitas intercaladas com fio metálico são mais
estáveis que nanofios encapsulados por nanotubos achatados.
[1] S. Iijima, Nature 354, 56 (1991). [2] C. Ataca, S. Cahangirov, E. Durgun, Y. R. Jang, and S. Ciraci. Phys.
Rev. B 77: 214413 ( 2008). [3] P. Ordejon, E. Artacho and J. M. Soler, Phys. Rev. B 53, 10441 (1996).
13
First principles study of defects in BN nanotubes
Andressa C. Bevilacqua, Rogério José Baierle
Universidade Federal de Santa Maria
Boron nitride (BN) is a compound formed by covalent bonds between B atoms and N atoms. In the crystal structure
it can be found in diferent phase, such cubic (c-BN), hexagonal (h-BN), wurtzite (w-BN) and rhombohedral (rBN). Similar to graphite h-BN can form two dimensional structures, which can be cut forming tubes. Otherwise,
c-BN has hardness similar to diamond, which is retained up to 2000o C while diamond discards to graphite at about
900o C. These properties make BN a promissor material for nanoelectronics in a hard environment. Here, we studied
mechanical, electronic and optical properties of BN nanotubes. Our study is directed not only to BN nanotubes
in the pristine form (no defects), but also when topological defects (vacancies) and dopant impurities (Carbon)
are present. The first principles calculations are based on the density functional theory with the generalized
gradient approximation for the exchange-correlation term. The calculations were performed using the SIESTA
computer code within gaussian functions to expand the Khon-Shan orbitals. We observe that C impurities have
low formation energies whereas vacancies have high formation energies. All the pristine BN nanotubes studied
are non magnetic semiconductor with a bang gap energy around 3.5 eV, which is almost independent of the tube
chirality and diameter. Carbon impurities introduce localized electronic levels into the band gap while vacancies
give magnetic moments to the BN nanotubes. Calculations for complex defects (carbon impurities and vacancies)
show that the formation of these complex defects have lower formation energies when compared to isolated defects,
indicating that these defects have great probability to occur. Double vacancies have formation energies somewhat
to the single vacancies and in the equilibrium geometry occur a reconstruction where a pentagon-octagon-pentagon
(5-8-5) structure is present. In the optimal geometry there is any dangling bond present and the magnetic moment
is zero but non spin polarized electronic levels are present in the band gap.
14
Electronic properties of BN nanotubes interacting with FeCl3 molecules and CrO3
Jerdson Serejo, Silvete Guerini
There is great interest in materials at the nanoscale, due to their potential applications in various scientific and
technological areas. Within the materials at the nanometer scale , the discovery of carbon nanotubes has provided
a new area of researsh and, since then , has attracted much interest due to their intrinsic properties and potential
applications . These systems have great mechanical strength, not to break or deform when bent or subjected to
high pressure , making these systems attractive for applications in nanotechnology. A large number of single-layer
nanotubes has been theoretically predicted , and some, such as boron nitride and BxCyNz has been successfully
synthesized. BN nanotubes are considered ideal systems for various applications in the field of nanoscale, not only
because of their unique electronic properties, but also due to the fact that it is chemically inert, has high thermal
conductivity and excellent mechanical properties. In this work we study the electronic and structural properties
of boron nitride nanotubes interacting with FeCl3 and CrO3 molecules through first-principles calculations. For
this we used the density functional theory implemented in the computer program SIESTA. Our results show that
introduction of molecules change the electronic properties, decreasing the energy gap and introducing new energy
levels in the gap region. Analyzing the charge transfer observed that molecules act as electron acceptor.
15
Soft and hard drugs interacting with carbon nanotubes
Jerdson Serejo, Eduardo Moraes Diniz
Chemical dependence is a serious problem in our society. The rehabilitation requires many professionals to treat the
addicted in psychological and clinical aspects. Nanotechnology can be used in the latter, where nanomaterials such
as carbon nanotubes could be used to help purge harmful substances. Although this is a treatment in increasing
use, there are few studies about how carbon nanotubes and drugs interact. In order to help to clarify this point,
here we report first principles calculations based on density functional theory of drugs (caffeine, heroin, LSD and
methamphetamine) interacting with zigzag or armchair carbon nanotubes. The calculations were performed using
the local density approximation with spin polarization as implemented by the SIESTA code. Ghost atoms were
employed in order to eliminate the basis set superposition error in the binding energy evaluation. The results shown
that the system drug plus carbon nanotube is more stable than the separate molecules, and the binding energies
are less than -0.08 eV. It was also found that there is a charge transfer from the carbon nanotube to the drug,
changing its electronic state. We also found that caffeine induces ferrimagnetism in the zigzag carbon nanotube.
These results may help in understanding how nanostructures can act in detoxification of the body through the
interaction with light or heavy drugs.
16
First principles calculations of structural, dynamical, and electronic properties of Type-I Ge
clathrates containing La guest atoms
R. L. Gonzalez, A. Antonelli
Instituto de Fı́sica “Gleb Wataghin,”Universidade Estadual de Campinas, Caixa Postal 6165, CEP 13083-970, Campinas,
São Paulo, Brazil
Caetano R. Miranda, M. A. Avila
Universidade Federal do ABC, Rua Santa Adélia, 166 Bangu 09210-170, Santo André, SP, Brazil
Type I clathrates La2 Ga6 Ge40 and La2 Zn3 Ge43 have been studied using density functional theory calculations.
Static parameters at T = 0 K, obtained by geometry optimization predict that these clathrates are thermodynamically more stable than their isolated bulk constituents and that their formation is energetically favorable [1].
Energy values show that the location of the Ge or Zn atoms in the clathrate frame affects the stability of the
compound. In particular, the system with Ga or Zn in 6c positions results thermodynamically more stable that
others [2,3]. Our calculations have revealed that La is located at off-center site in 2a positions. This off-center
displacement of the “guest”atoms depends on the relative positions of the Ge or Zn atoms and affects the charge
and electronic densities of these materials. The phonon dispersion relation of these clathrates was also calculated.
Of particular importance is the occurrence of rattling La modes that cut through the acoustic modes in the phonon
dispersion. Moreover, the disorder of the “guest”position is very complex and produces symmetry-breaking.
[1] N.P. Blake, D. Bryan, S. Latturner, L. Møllnitz, G.D. Stucky, H. Metiu, The Journal of Chemical Physics
114 (2001) 10063.
[2] C. Gatti, L. Bertini, N.P. Blake, B.B. Iversenl, Chem. Eur. J. 9 (2003) 4556
[3] S. Johnsen, A. Bentien, G.K.H. Madsen, M. Nygren, B.B. Iversen, PHYSICAL REVIEW B 76 (2007) 245126.
17
Study of structural and electronic properties of Materials Based on Aluminum Nitride in 1-D and
2-D
Edward F. de Almeida Jr, Fernando de B. Mota, Caio M. C. Castilho
Universidade Federal da Bahia - Brasil
G. K. Gueorguiev, A. Kakanakova-Georgieva
Universidade de Linköping - Suécia
Theoretical calculations focused on the stability of an infinite hexagonal AlN (h-AlN) sheet and its structural and
electronic properties were carried out within the framework of DFT at the GGA-PBE level of theory. For the
simulations, an h-AlN sheet model system consisting in 96 atoms per super-cell has been adopted. For h-AlN, we
predict a lattice parameter of 1.82 Å and an indirect gap of 2.81 eV as well as a cohesive energy which is by 6 per
cent lower than that of the bulk (wurtzite) AlN which can be seen as a qualitative indication for synthesizability of
individual h-AlN sheets. Besides the study of a perfect h-AlN sheet also the most typical defects, namely, vacancies,
anti-site defects and impurities were also explored. The formation energies for these defects were calculated together
with the total density of states and the corresponding projected states were also evaluated. The charge density
in the region of the defects was also addressed. Energetically, the anti-site defects are the most costly, while the
impurity defects are the most favorable, especially so for the defects arising from Si impurities. Defects such as
nitrogen vacancies and Si impurities lead to a breaking of the planar shape of the h-AlN sheet and in some cases
to formation of new bonds. The defects significantly change the band structure in the vicinity of the Fermi level in
comparison to the band structure of the perfect h-AlN which can be used for deliberately tailoring the electronic
properties of individual h-AlN sheets. The study nanoribbons with the same base atoms of the infinite sheet was
still held, but now there were only periodic conditions in the x direction. Inserted hydrogen atoms, fluorine and
chlorine in these nanoribbons realized the full study of structural and electronic properties as the two-dimensional
sheet. It was possible to verify the stability of the materials, as well as the length of the bonds of the inserted tape
atoms.
18
Effect of disorder on the mechanics and electronics properties of BCN structures.
David Joseph Pereira Beserra, Jonathan da Rocha Martins
Universidade Federal do Piauı́
In this work we studied the effect of the disorder on the mechanics and elastics properties of BCN structures through
first-principles calculations implemented into SIESTA code. The use of this method consists in some approximations
as Born-Oppenheimer, Pseudopotential theory, Bloch’s theorem, and the two theorems of Hohemberg and Kohn,
which, together, compose the basis of the DFT (Density Functional Theory).
Thereby, it was applied forces in determined directions of graphene with the intention of to cause deformations in
the structure. Alterations in the structure may modify in a significative way the electronics properties of materials
as graphene, for instance. Mechanics properties of doping graphene by Boron and Nitrogen has been studied
nowadays and has showed many interesting possibilities of application (Peng, Q. et. al. Acta Mech. 223: 2591,
2012). In this work, graphene was doping with Boron (B) and Nitrogen (N) which was applied a strain in selected
samples. Furthermore, was calculated the elastics constants of each sample. The proposal samples have the same
concentration of Carbon, Boron and Nitrogen. However, they differ by the positional disorder degree of the atoms
into material. One of the objectives is evaluate the changes in the behavior of the elastics constants of each sample
according with the positional disorder of chemical species.
We find that the elastic constant decreases with the increase concentration of BN when compared with pure
graphene. The next step is analyse the effect with many samples and verify the alterations on the electronic
properties in each sample.
19
Study of structural reconstruction of doped graphene
Ramiro Marcelo dos Santos, Jonathan da Rocha Martins
The density functional theory is of wide application, for example, in applications in condensed matter. A very
common application of this theory is the study of two-dimensional crystals such as graphene. Graphene is a twodimensional structure with a thickness of one atom. This structure was first isolated by two russian scientists
working at the University of Manchester, England, Andre Geim and Konstantin Novoselov were the first to isolate
graphene. This work won the Nobel Prize in 2010. Graphene is a semimetal with zero band gap and its properties
are well known. Graphene has interesting mechanical properties and changes in its electronic properties have
been proposed in literature (Saito, R. textit Physical Review B. 46:1804, 1992 et al..; Liang, L. textit et. al.
Physical Review B 88:035420, 2013). Structural changes of graphene have been proposed as a possibility to change
the electronic properties of the material, opening many possibilities for applications primarily in nanoelectronics.
Some defects in the graphene can significantly alter the electronic properties of this two-dimensional material. The
gap of this material can be achieved by defects in its structure. One of the types of defects of great interest is
the symmetric monovacancy (s-MV) and the reconstruction monovacancy (r-MV). The effects of these structural
defects have been studied and some interesting results have been obtained in graphene (Robertson, AW et al. ACS
Nano, 7: 4495, 2013). The objective of this work is to study the effects of the defects in graphene doped with some
atoms as boron and nitrogen - BCN (with segregated graphene on BN), which are currently being studied and may
be promising for applications in nanodevices.
20
Thermal Expansion Measurements with Subatomic Resolution
Cesar Augusto Sônego, Mariano de Souza
IGCE, Unesp - Univ Estadual Paulista, Departamento de Fı́sica, Rio Claro (SP), Brazil
In the study of the physical properties of solids, measurements of the thermal expansion coefficient enable the
exploration of several fundamental aspects of phase transitions. For instance, combining thermal expansion (αi )
with specific heat (C) data and employing the Ehrenfest relation [1],
(
)
dTc
∆αi
= Vmol Tc
(1)
dPi Pi −→0
∆C
where Vmol refers to the molar volume, Tc to the phase transition critical temperature and the index i denotes the
crystallographic direction; it is possible to determine the pressure dependence of the critical temperature (dTc /dPi )
of a second-order phase transition. Similarly, in the case of a first-order phase transition, by measuring the volume
change (∆V ) associated with the phase transition and knowing dTc /dP it is possible to obtain the entropy change
via Clausius-Clapeyron equation [1],
dTc
∆V
=
(2)
dP
∆S
Interestingly enough, thermal expansion measurements employing the capacitive method enable to achieve a
maximum resolution of ∆l /l = 10−10 [2]. Essentially, in this method, the dilatometer cell is constituted of a parallel
plate capacitor, being the sample to be investigated mechanically linked to the capacitor. Thus, measuring the
capacitance as a function of temperature one can directly obtain the change of the sample length (l) along the
crystallographic direction of interest using the well-known formula for the parallel plate capacitor [3],
ϵ0 A
(3)
d
where ϵ0 refers to the vacuum permittivity, A to the area of the plates of the capacitor and d is the distance
between the capacitor plates. These measurements are carried out using a capacitance bridge with a maximum
resolution of 10−6 pF. The temperature of the sample is changed using a Pulsed Tube Refrigerator (Teslatrom PT)
system supplied by Oxford Instruments. Experiments in the temperature window 1.4 K < T < 300 K and under
magnetic fields up to 12 T can be performed employing such a system.
In this contribution we present the principle of work of a quartz cell dilatometer with a maximum resolution of
0.01 Å [4], preliminary results and perspectives will be also discussed.
C=
This work was supported by the São Paulo Research Foundation (Fapesp) (Grants 2011/22050-4) and National
Research Council (CNPq) (Grants 308977/2011-4).
Bibliography
[1] H.B. Callen, Thermodynamics and an Introduction to Thermostatistics, Ed. John Wiley and Sons Inc, Second
Edition, (1985).
[2] R. Pott, R Schefzykt, Review of Scientific Instruments 16, 444 (1983).
[3] P.A. Tipler, G. Mosca, Physics, Vol. 2, Ed. LTC, (2006).
[4] R.S. Manna, B. Wolf, M. de Souza, M. Lang, Review of Scientific Instruments, 83, 085111 (2012).
21
A first principles study of the oxidation process of InP and InAs nanowires
Mailing Berwanger, Paulo Cesar Piquini
Universidade Federal de Santa Maria - UFSM
Cláudia Lange dos Santos
Centro Universitário Franciscano - UNIFRA
Semiconductors nanowires are one-dimensional nanostructures that are among the most studied in the last decades.
The influence of the growth temperature and the flow of precursors in the morphology of nanowires was studied
by various investigator [DICK et al., 2006; SEIFERT et al., 2004; TCHERNYCHEVA et al., 2007]. Nanowires
and other structures can be produced in direct contact with atmospheric gasses, in particular oxygen molecules.
Therefore, there is a great interest in the possible contributions of this gaseous environments on the properties of
the nanowires. Althoug the presence of an oxide layer ate the surface of nanowires is frequently observed, there
are few theoretical studies of theirs influence on the properties of the nanowires. The present work study two
different stages of the oxidation process of InP and InAs nanowires: (i) the initial stages, when an unsaturated
InP and InAs nanowires is in the presence of an gaseous oxygen envirounment, and (ii) a possible final situation,
where the external layers of a InP and InAs nanowires have already been oxidized. The study is performed through
molecular dynamics simulations (at 300K), using the first-principles Density Functional Theory to determine the
atomic forces, and the Newtonian equations of motion to the dynamical study of the systems. All calculations
are performed using the computational code VASP. Our results show the dynamics of the bond breaking of the
oxygen molecules in the gaseous environment by the atoms at the nanowires surfaces, which is followed by the
incorporation of the oxygen atoms in the outermost layers of the InP and InAs nanowires. Subsequent cycles
of molecular dynamics, shortly after a transient phase, shows an amorphous structure fo the outer layers of the
nanowires, which is in agreement with experimental observations in the literature. For the simulations of an already
oxidized nanowire, the molecular dynamics results allow us to determine the most common chemical bonds resulting
from the interaction of the oxygen and nanowire atoms. Statistically representative uncorrelated configurations,
obtained through the use of a time correlation function, were selected and the projected density of states was
analyzed, which allow us to determine the contribution of the different chemical bonds to the electronic structure
of the oxidized nanowires. Keywords: Density Functional Theory. InP and InAs nanowires. Oxidation.
22
Theoretical study of the interaction of carbon nanotube with hydroxyapatite: A first principles
study
W. Knupp, M. Mir, I. Camps
Laboratório de Modelagem Computacional - LaModel. Instituto de Ciências Exatas - ICEx, Universidade Federal de
Alfenas - Unifal-MG.
Our bones are composed of organic and inorganic phases. The hardness characteristics of bones are transmitted by
mineral components, being one of the main components the apatite. Its elasticity comes from organic substances
such as collagen and small quantities of elastin. On the other hand, the compact bone presents itself as a solid
mass prepared in layers, suggesting us that the proposed materials to be incorporated by bone structure should
present similar structure. The apatite is a mineral that belongs to the group of phosphates and that has several
applications in the development of new materials. Among its variants, we found the hydroxyapatites (HAP), which
have chemical and physical properties that allow the bone replacement, making this material the one that most
closely resembles the mineral phase of bone and human teeth. However, the HAP has poor properties compared to
bone tissue, which limits its use in clinical applications, especially in areas that need high mechanical effort. Because
of these characteristics, we studied, through computational simulation based on Density Functional Theory (DFT),
the interaction of HAP with carbon nanotubes (CNTs). Here we used single wall carbon nanotubes (SWCNT) pure
(SWCNTS-P) and functionalized with organic carboxyl groups (SWCNT-COOH) and hydroxyl (SWCNTS-OH)
in different concentrations of functionalization. This, because the CNTs should provide to the HAP mechanical
properties more relevant in comparison to human bones. Due to strong chemical stability of nanotubes its interfacial
interaction with the HAP matrix may be affected. The proposed solution, to further increase both dispersion and
interaction, was the functionalization of nanotubes. We observed that we need to take care with the dispersion of
CNTs in the material and that the interfacial connection between the CNTs and the material is strongly affected
by the amount of organic groups introduced in the nanotubes surfaces. We acknowledge financial support of
FAPEMIG.
23
Estudo das propriedades estruturais e vibracionais do carvacrol através de cálculos computacionais
usando a Teoria do Funcional da Densidade
B.G. Cruz, M.N.L. Gonçalves, R.N. Santos, A.M.R. Teixeira, D.M. Sena Junior
R.R.F. Bento, J.L.B. Faria
Universidade Federal do Mato Grosso
P.T.C. Freire
O carvacrol é um fenol monoterpenóide quimicamente denominado (5-isopropil-2-metilfenol), possui fórmula molecular C10 H14 O e está presente em muitos óleos essenciais de plantas, especialmente nos gêneros Origanum e Thymus
[1]. O carvacrol isolado reduz as contorções abdominais induzidas por ácido acético e inibe as fases iniciais (dor
neurogênica) e tardias (dor inflamatória), apresentando ação analgésica local [3]. Esse monoterpeno possui também
uma grande variedade de atividades biológicas benéficas, tais como antibacteriana, antifúngica e antioxidante [2-3].
Neste trabalho realizamos um estudo das propriedades estruturais e vibracionais do carvacrol através de cálculos
computacionais usando a Teoria do Funcional da Densidade. Uma descrição tanto geométrica (distâncias, ângulos
e diedros de ligação) como energética (energia da rede e frequências de vibração) é apresentado neste trabalho.
Além disso, as vibrações moleculares foram analisadas em termos de distribuição de energia potencial, utilizando o
programa VEDA. Para o melhor de nosso conhecimento, este é o primeiro estudo onde uma atribuição completa das
vibrações moleculares junto com a distribuição de energia potencial está sendo apresentado para esta substância
que está presente em uma grande variedade de óleos essenciais.
Referências:
[1] BAKKALI, F.; AVERBECK, S.; AVERBECK, D.; IDAOMAR, M. Food Chem Toxicol, v. 46, n. 2, p.
446-475.
[2] GUIMARÃES, A. G.; OLIVEIRA, G. F.; MELO, M. S.; CAVALCANTI, S. C.; ANTONIOLLI, A. R.;
BONJARDIM, L. R.; SILVA, F. A.; SANTOS, J. P.; ROCHA, R. F.; MOREIRA, J. C.; ARAÚJO, A. A.; GELAIN,
D. P.; QUINTANS-JÚNIOR, L. J. Basic Clin Pharmacol Toxicol, v. 107, n. 6, p. 949-957.
[3] ULTEE, A.; BENNIK, M. H.; MOEZELAAR, R. Appl Environ Microbiol, v. 68, n. 4, p. 1561-1568.
24
Estudo de espectroscopia vibracional do (E)-cariofileno por cálculos computacionais usando a
Teoria do Funcional da Densidade
M.N.L. Gonçalves, B.G. Cruz, R.N. Santos, A.M.R. Teixeira, D.M. Sena Junior
P.T.C. Freire
O (E)-cariofileno de fórmula molecular C15 H24 , é um sequiterpineno bicı́clico formado por três subunidades de
isopreno. Essa substância molecular é encontrada em óleos essenciais de algumas plantas como: cravo (Eugenia
Caryophyllata), pimenta - preta (Piper nigrum), erva de são João (Aregatum Conyzoides); maconha (Cannabis
sativa) e óleo resina de copaı́ba (Copaifero sp). Informação farmacológica refere-se a esta substância como sendo
anti-inflamatória, antitumoral, antialérgica, bactericida e repelente [1]. Essa substância possui também ação terapêutica nas infecções produzidas por estafilococos especialmente quando aplicadas em feridas infectadas [1]. A
literatura reporta alguns estudos de espectroscopia em alguns óleos essenciais que tem o (E)-cariofileno como um
dos seus compostos majoritários. Porém, até o presente momento não tem sido reportado cálculos teóricos das
propriedades vibracionais para este composto. Neste trabalho realizamos um estudo de espectroscopia vibracional
do (E)-cariofileno por cálculos computacionais usando a Teoria do Funcional da Densidade (DFT). Usamos o programa Gaussian 03 empregando o método DFT com o funcional hibrido B3LYP e o conjunto de base 6-31G (d,p)
para calcular as frequências vibracionais e os espectros teóricos Raman e infravermelho deste composto. Em adição,
as vibrações moleculares foram analisadas em termos da distribuição de energia potencial, utilizando o programa
VEDA.
Referência:
[1] AZAMBUJA, W. Essential Oils. São Paulo 2009.
25
Self-reconstruction and predictability of bonds disruption in twisted graphene nanoribbons
Eduardo Moraes Diniz
Graphene nanoribbons are of great interest due to their applications in nanosized circuitry, where the former can
undergo several mechanical deformations, as for example strains and twists. Although there are many investigations
about twisted graphene nanoribbons, no density functional calculations are presented concerning their structural
integrity when these ribbons are twisted by large angles. In order to investigate this, here are reported first principles
calculations on twisted graphene nanoribbons. The results show that for most structures, the system undergoes a
transition where it self-reconstructs to the original nanoribbon after twisting beyond a specific angle. This twist
angle depends linearly on the nanoribbon length and has a non-linear behavior with the width. Also one finds
that it is easier to twist an armchair graphene nanoribbon than a zigzag one when both have the same width and
length. In addition, it was performed a simple classical model by applying tensile strain where its agreement with
the density functional calculations becomes better for wider graphene nanoribbons, indicating that it is possible
to estimate the maximum twist angle knowing only geometric data (length and width). This information could be
used in prevention ruptures due to twists of the graphene nanoribbons present in nanosized circuitry with flexible
shape.
26
Peierls distortion in nanowires encapsulated by carbon nanotubes
Rosinete Bernardes Rodrigues, Eduardo Moraes Diniz
Encapsulation of nanowires made of transition metals by carbon nanotubes is a very common subject in both
theoretical and experimental aspects. Theoretically, it was find that independent on the chemical species of the
transition metal, the magnetic moment is always reduced when the nanowire is encapsulated by a carbon nanotube.
However, all calculations presented in the literature concern only on regular-spaced nanowires and it is well know
that linear wires exhibit a dimerization (Peierls distortion) in order to lower the energy. Such dimerization can
provoke changes in the electronic structure of the nanowire, as for example a metal-semiconductor transition. In
order to investigate how a dimerized nanowire behaves in comparison with a non-dimerized one, here we report
first principles calculations based on the density functional theory using the generalized gradient approximation for
the exchange-correlation potential of nanowires made of iron, cobalt, chromium or nickel encapsulated by zigzag or
armchair carbon nanotubes. The calculations shown that for some systems, the dimerized state of the encapsulated
nanowire is more stable. Also one find that for a dimerized nanowire, the magnetic moment reducts when it is
encapsulated, but in a smaller amount in comparison with a non-dimerized nanowire. Some systems exhibit a
bi-stability between dimerized and non-dimerized geometries and the energy barrier was determined from one state
to the other one. Such results can be used to understand possible differences between experimental and theoretical
data and to predict new properties of encapsulated nanowires.
27
Evolution of Topological Surface/Edge States in Bismuth Nanostructures
Erika N. Lima, Tome M. Schmidt
Universidade Federal de Uberlândia
In recent years, topological insulators (TI) have been extensively studied. These new materials are a new class of
quantum materials in which time-reversal symmetry, relativistic effects and an inverted band structure result in
the ocurrence of metallic surface states that are higher-dimensional similar of the edge states that characterize a
quantum spin Hall (QSH) insulator [1,2]. In the QHS system, the bulk is gapped and insulating, while there are
gapless states on the edge or on the surface carrying a spin current. This phase characterized by the Z2 topological
number ν=0,1, which corresponds to ordinary and topological insulators, respectively. In this work, employing
first-principle calculations which is a powerful tool for the investigation of the physics of topological insulators. We
studied the electronic structure of ultrathin films and nanorribons of bismuth, focusing on the appearance of surface
and edge states that are topologically protected. These surface states and edge states appear in (111)-orientation
ultrathin films and (110)-orientation ribbon, respectively. In all structures, we investigate the influence of spin
orbit coupling and analyze spin polarization of the states at the boudanries and edges of the material. Ours results
show that these states are strongly spin polarized and their properties are found to be nontrivial.
[1] Yu M. Koroteev.et al,Physical Review Letters 93, 046403 (2004).
[2] M. Wada et al, et al,Physical Review B 93,121310 (2011).
28
Strong correlations in density-functional theory: A model of spin-charge and spin-orbital
separations
Daniel Vieira
Departamento de Fı́sica, Universidade do Estado de Santa Catarina
Spin and charge use to be treated as fundamental properties of ordinary electrons. However, when confined
in one dimension, interacting electrons display the unusual property of separating their spin and charge into two
independent quasiparticles: spinons and chargons. Both behave just like ordinary electrons, but: spinons have spin1/2 and no electrical charge, while chargons are spinless charged electrons. Recently, an additional fractionalization
was shown to occur [1,2]: The spin-orbital separation, for which spin and orbital degrees of freedom are decoupled
to form the orbitons – particles with no spin and charge, carrying solely the orbital information. The Kohn-Sham
(KS) formalism of density-functional theory (DFT), by construction, retains the spin, charge and orbital degrees of
freedom together, once it considers an auxiliary system of noninteracting particles. In contrast, it has been shown
that the separation into spinons and chargons is decisive when performing DFT calculations of one-dimensional
(1D) strongly-correlated density distributions [3]. In this work, we extend the investigation and propose a model
for the spin-orbital separation in DFT. Specifically, we deal with two exact constraints of exchange-correlation
(XC) density-functionals: (i) The constancy of the highest occupied (HO) Kohn-Sham eigenvalues upon fractional
electron numbers, and (ii) their discontinuities at integers. These constraints are usually not satisfied even by
modern approaches, and are the cause of dramatic errors when describing any generic situation involving transport
of charges. By means of 1D discrete Hubbard chains and 1D H2 molecules in the continuum, we find that spincharge separation yields almost constant HO KS eigenvalues, whereas the spin-orbital counterpart can be decisive
when describing derivative discontinuities of XC potentials at strong correlations.
[1] K. Wohlfeld et al., Phys. Rev. Lett., 107, 147201 (2011).
[2] J. Schlappa et al., Nature, 485, 82 (2012).
[3] D. Vieira, Phys. Rev. B, 86, 075132 (2012).
29
Meloxicam molecules interacting with carbon nanostructures
Ivana Zanella, Daniela Almeida, Solange B. Fagan
The use of nanoscale systems, in pristine or functionalized form, as sensors / filters chemical and biological is a
vast area of study and of great importance. With some nanometers in diameter, the size of the nanostructures
are perfect for interacting with DNA and proteins, which already involve a wide range of studies and has added
many efforts, especially those related to drug associated with of cancer and AIDS treatments, as well as use in
controlled drug delivery (DOALATABADI, 2011; RAFFA, 2008). Preliminary studies have associated drugs and
vitamins the carbon nanostructures surface, which have a high capacity to cross the blood-brain barrier, which
characterizes these compounds as ideal carriers for drugs or other biological molecules into the organism ( RAFFA,
2008). The central idea of this work is to analyze the behavior of these nanostructures interacting with meloxicam, a
nonsteroidal anti-inflammatory drug. The structural and electronic properties of this systems was analyzed through
first first-principles calculations, based on the density functional theory (DFT). Our results show that interaction
between carbon nanostructures and meloxicam molecules occurs via physical adsorption, with binding energies of
0.12 - 0.40 eV, without changes in structural and electronic properties of the systems. Thus, combining meloxicam
molecules with fullerene and carbon nanotubes we intend to signal new chemical and biological structures that
may contribute to the treatment of Alzheimer’s and osteoarthritis diseases (IANISKI, 2012).
DOALATABADI, Japar ; et al.; Quercetin delivery into cancer cells with single walled carbon nanotubes.;
Internacional Journal of Bioscience; 1; 21 - 25; 2011.
IANISKI, Francine; et al.; Protective effect of meloxicam-loaded nanocapsules against amyloid- peptide-induced
damage in mice. Behavioural Brain Research; 230; 100-107; 2012.
RAFFA, Vittoria; et al. ; Can the properties of carbon nanotubes influence their internalization by living cells?;
Science Direct; 46; 1600-1610; 2008.
30
Structural and optical properties of small clusters of CuSe
Paulo Cesar Piquini, Alex Schmidt, Raisi Baldez, Luianne Rodrigues dos Santos
UFSM- RS - Brasil
Atomic clusters are aggregates from two to thousand atoms with a high surface to volume ratio. This fact influences
directly their properties both through direct effects of electronic surface states and via quantum confinement
effects, with their properties being different from those presented by their bulk forms. Their properties will vary
with the number of atoms, with the assumed geometric shape, with its ionization state etc. These variations of
the cluster properties provide a way to obtain materials whose characteristics can be selected in a very specific
manner. This makes the study of clusters an extremely rich field with great opportunities for advanced technological
applications. Recently, the search for materials for photovoltaic applications has been expanded to many different
compounds. Thin films and nanoparticles of copper (Cu) and selenium (Se) are among the most studied materials
for photovoltaic applications [1]. Copper selenide is a semiconductor that appears in different stoichiometric
compositions (Cu2Se, Cu3Se2, Cuse, and CuSe2), not stoichiometric (Cu2-xSex ) and various crystallographic
forms[2]. In recent years there has been a breakthrough in the studies of CuSe clusters due to their fascinating
properties and wide applications in solar cells, gas sensors, thermoelectric converters, etc [3-4]. In this work
we use the genetic algorithm method coupled to density functional theory calculations to determine the lowest
energy configurations of CuSe (copper selenide). Once the most stable structure is determined, we then study the
absorption spectra of these clusters in order to understand the evolution of their optical properties with size. The
optical properties will be determined using the time-dependent density functional theory.
[1] S.R. Gosavi, N.G. Deshpande, Y.G. Gudage, Ramphal Sharma Journal of Alloys and Compounds, 2008, pp.
344-348
[2] Dhanam M, Manoj PK, Prabhu RR J. Crystal Growth(2005), pp. 280-425
[3] Y. Li, S. Luo, L. Yang, C. Liu, Y. Chen, D.S. Meng Electrochimica Acta, 83 (2012), pp. 394-401
[4] S.K. Haram, K.S.V. Santhanam Thin Solid Films, 238 (1994), p. 2
31
Propriedades Estruturais e Eletrônicas do Grafeno depositado sobre Si(111)-B
Rodrigo Torquato Jr
Universidade Federal Fluminense
Roberto Hiroki Miwa
Pedro Venezuela
Neste trabalho investigamos as propriedades estruturais e eletrônicas de uma ou duas camadas de grafeno depositadas sobre a superfı́cie de Si(111) dopada com Boro, Si(111)-B. É conhecido experimentalmente que quando
a superfı́cie de Si(111) é dopada com a impureza de boro não ocorre reconstrução. Desta forma, esta superfı́cie
mantém sua estrutura hexagonal e portanto é uma boa candidata para ser utilizada como substrato do grafeno. Realizamos cálculos de primeiros princı́pios baseados da teoria do funcional da densidade. Os cálculos foram realizados
utilizando a expansão das funções de ondas em ondas planas e pseudopotenciais ultrasoft. Em geral, utilizamos a
aproximação do gradiente generalizado (GGA) para o termo de correlação e troca mas testes incluindo interação
de Van der Walls também foram realizados. A partir destes cálculos podemos determinar as alterações estruturais
que ocorrem no grafeno quando depositado sobre esta superfı́cie. Podemos também investigar as alterações nas
propriedades eletrônicas do grafeno, em particular temos interesse em determinar como os cones de Dirac são modificados. Numa parte posterior do trabalho iremos calcular as imagens de microscopia de tunelamento de varredura
(STM) e as propriedades vibracionais do grafeno depositado neste substrato, estes cálculos podem vir a ser muito
úteis para auxiliar na caracterização deste material.
32
Interaction of hemoglobin with cyanide through via ab initio simulation
Patrı́cia Viera de Oliveira, Mariana Zancan Tonel, Solange Binotto Fagan
The work is based on the tragedy of Kiss Nightclub in Santa Maria-RS, which 242 victims died due to inhalation
of toxic gases, especially cyanide gas released by combustion of sponges, wood and synthetic polymers in general.
In this way, we selected cyanide gas to interact with hemoglobin aiming to understand the resulting electronic and
structural propertiesof the systems, via SIESTA code [1].
Hemoglobin is a tetrameric protein present in erythrocytes where its main function is to transport oxygen
from the lungs to the peripheral tissues, being able to use their efficiency up to 90 percent of its power in oxygen
transport [2]. The inhalation of cyanide gas causes a rapid and extensive inhibition of the mitochondrial electron
transport chain, in step citrossomo c oxidase, cyanide is one of the most potent and rapid toxins known. The
cyanide gas binds to Fe3+ of the heme a3 of cytochrome c oxidase, which catalyzes the final step of the electron
transport chain, mitochondrial respiration and energy production ceases, and cell death occurs rapidly [3].
The obtained results, by means of ab initio simulations, of the six different configurations studied show that
the most stable one has binding energy of -3.22 eV and binding distances of 2.03 Å, through the Fe atom of the
hemoglobin and the cyanide molecule.
It was observed that the Fe atom in hemoglobin moves relative to the surface to interact with cyanide (may
even be removed from the porphyrin ring), proving that there is a strong interaction between these molecules.
Considering the spin polarization is observed that the isolated hemoglobin/cyanide gas has 4miB/1miB and when
they are interacting this value is 5miB. Also, the charge transfer occurred from the cyanide molecule to the
hemoglobin with values around 0,197 (e-) for the most stable configurations. The electronic levels are modified
after the interaction of hemoglobin with the cyanide gas, due to the high hybridization because of the chemical
bond between the systems.
References:
[1] SOLER, J. M.et al. The SIESTA method for ab initio order-N materials simulation.J. Physics: Condensed
Matter, v. 14, p.2745-2779, 2002.
[2] BERG, Jeremy M. et al. Bioquı́mica. 6 ed.Rio de Janeiro: Guanabara Koogan S.A., 2007.
[3] DELVIN, Thomas; MICHELACCI, Yara. Manual de Bioquı́mica. São Paulo: Blucher, 2007.
33
Sistemas quânticos unidimensionais como laboratórios para o desenvolvimento da Teoria do
Funcional da Densidade
Mateus B. P. Querne, Daniel Vieira
Departamento de Fı́sica, Universidade do Estado de Santa Catarina
A Teoria do Funcional da Densidade (DFT) se tornou uma das principais ferramentas modernas para o cálculo
da estrutura eletrônica da matéria. Formalmente exata a partir dos teoremas originais, o sucesso de aplicações
DFT depende de aproximações precisas para o funcional de troca e correlação, em conjunto com estratégias de
implementação computacionalmente viáveis. Nesse contexto, propomos aqui a utilização de sistemas quânticos
unidimensionais como laboratórios teóricos, mais simples de se implementar e que ainda podem fornecer importantes
pistas para uma descrição mais precisa de sistemas tridimensionais. Especificamente, aplicamos uma aproximação
local da densidade dependente de spin (LSDA) a modelos de átomos unidimensionais. Como essa LSDA é incorreta
para sistemas monoeletrônicos, ou seja, sofre de um erro de auto-interação, incluı́mos a correção de auto-interação
ADSIC, mantida como um funcional explı́cito da densidade via ideia de densidade orbital média. Encontramos que
a abordagem ADSIC tende a reduzir fortemente os erros apresentados pela LSDA, sobretudo em se tratando dos
potenciais de ionização obtidos via autovalores Kohn-Sham mais altamente ocupados. Apesar disso, o funcional
ADSIC é caracterizado pela inconsistência em tamanho, levando a resultados indesejáveis em processos como os
de dissociação molecular. Por essa razão, expomos também uma abordagem que visa contornar a inconsistência
da ADSIC, estendendo a análise a moléculas unidimensionais.
34
A Combined DFT and PCM study of the UV-VIS spectra of dimethoxy curcumin in different
solvent environments
Tárcius Ramos, Sylvio Canuto
Instituto de Fı́sica da USP
Solvent effects on spectroscopic, structural and electronic properties of molecules and biomolecules are one of the
most important topics in physical chemistry. Well known as turmeric, dimethoxy curcumin (DMC) is a pigment
widely used as an aromatic stimulant and spice. Recently it has been recognized to present also pharmacological
activities such as antioxidant and antitumor [1]. Apparently, their biological properties are enhanced with the
absorption of electromagnetic radiation [2,3] in the visible-ultraviolet region [4]. From the spectroscopic point
of view, an important feature observed experimentally is a large Stokes shift. This large difference between the
absorption and emission is peculiar in one of the tautomeric forms. This work is thus devoted to a theoretical
calculation of the UV-VIS spectra in gas phase and in two solvents (acetonitrile and cyclohexane) using timedependent density functional theory (TDDFT) and Polarized Continuum Model (PCM). The ground state geometry
is obtained for five conformers, in the keto and enol forms [5], using B3LYP/6-31+G(d,p) calculations. Next, the
excitation energies were calculated using different functionals. These functionals are of two types: including (LCwPBE, CAM-B3LYP, wB97XD) or not (B3LYP, O3LYP, PBE1PBE, BHandHLYP) long range corrections. All
calculations of the absorption spectra were performed using the 6-311++G(2d,2p) basis set. The results show that
the excitation energy is underestimated for B3LYP, O3LYP and PBE1PBE. For this case, when solvent effects
are included in the calculations, the excitation energies are red shifted and less agreement with the observed
experimental maximum. In the low-energy part the calculated spectrum in solvent is in found to be in good
agreement with experiment, especially when using the CAM-B3LYP/6-311++G(2d,2p) method.
[1] A. Banerjee et al Chem. Biol. Int. 174, 134 (2008).
[2] T. A. Dahl et al Photochem. Photobiol. 59, 290 (1994).
[3] A. B. Hegge et al. Euro. J. Pharma. Sci. 47, 65 (2012).
[4] A. Barik and K. I. Priyadarsini, Spectr. Chim. Acta A 105, 267 (2013).
[5] R. Benassi et al. Journal of Molecular Structure 892, 168, (2008).
35
Classificação das vibrações moleculares do éter metil timol através de cálculos teóricos de quı́mica
quântica
R.N. Santos, B.G. Cruz, M.N.L. Gonçalves, A.M.R. Teixeira, D.M. Sena Junior
P.T.C. Freire
O éter metil timol também conhecido como metil timol possui fórmula molecular C11 H16 O. Esse composto é encontrado em diversos óleos essenciais de plantas nativas do Nordeste do Brasil. O éter metil timol apresenta-se como
composto majoritário nos óleos essenciais da Lippia sidoides (Alecrim pimenta) e a Origanun vulgare (orégano).
Neste trabalho realizamos cálculos teóricos de quı́mica quântica empregando o método da Teoria do Funcional
da Densidade (DFT do inglês Density Functional Theory) para obter a classificação das vibrações moleculares do
éter metil timol. Usamos o programa Gaussian 03 para a realização dos cálculos DFT. Os cálculos de otimização
da estrutura molecular e das frequências vibracionais foram realizados usando o funcional de correlação de LeeYang-Parr, B3LYP e o conjunto de base 6-31G (d,p). As vibrações moleculares foram analisadas em termos da
distribuição de energia potencial, utilizando o programa VEDA. Na região de 50 cm−1 à 1000 cm−1 identificamos as
vibrações do tipo torção e as deformações do anel aromático. Foi possı́vel também observar a localização acentuada
dos modos de deformação angular do grupo funcional CH3 : as vibrações do tipo wagging do CH3 são observadas
entre 1400 cm−1 a 1500 cm−1 e as vibrações do tipo scissorig do CH3 aparecem entre 1500 cm−1 a 1600 cm−1 . As
bandas originadas a partir de estiramento dos grupos funcionais CH e CH3 são observadas nas regiões entre 2800
cm−1 a 3200 cm−1 . Vale ressaltar que pela primeira vez está sendo reportado a atribuição completa das vibrações
moleculares do composto éter metil timol.
36
Double-walled Carbon Nanocones: Stability and Electronic Structure
Elias Alves, T. Guerra, A. Almeida, T. Silva, S. Azevedo
Universidade Federal da Paraı́ba
Multi-walled carbon nanostructures, some well-known examples are the graphite, nanotubes, and nanocones, which
have been extensively studied by theoretical and experimental procedures due to the fact that they are believed
to be unique materials which may be used as components in the creation of many future nanodevices [1, 2]. Kim
et al have shown that multi-walled carbon nanocones can be synthesized by means of the method of chemical
vapor deposition, and that such structures exhibit interesting electronic and magnetic properties which open the
possibility of application in electronics and spintronics, respectively [3]. Following this line of thought, we apply
first-principles calculations to investigate the electronic structures and stability of double-walled carbon nanocones.
The studies involve double-walled carbon nanocones with pentagon or square in the tip of the inner and outerwalled cones. We consider two types of double-walled nanocones. The first part of the work we have analyze the
stability and electronic structure of double wall carbon nanocones trying to identify which distance entres its apex
is the most stable. We used concentric cones and we rotate the external nanocone at an angle approaching the
configuration of Bernal graphene. In the second part, with the most stable distance found, we calculate the external
nanocone rotations following the Moiré patterns, where only some angles are possible to obtain the pattern and
find which one makes the configuration of double wall carbon nanocone more stable. We also analyze the density
of states with and without spin polarization, beyond the behavior of the heights of the inner and outer nanocones.
[1] Klaus. Carbon 33, 915 (1995).
[2] M. Munõz Navia, J. Dorantes-Dávila, M. Terrones and H. Terrones. Physical Review B 72, 235 (2005).
[3] Y. A. Kim, T. Hayashi, K. Osawa, M. Endo and M.S. Dresselhaus. Chemical Physics Letters 367, 537,
(2003).
37
Extended line defect in graphene nanoribbons
Thiago Brito Gonçalves Guerra, Sérgio André Fontes Azevedo
UFPB - PB - Brasil
Graphene nanostructures have been a subject intensively studied in recent years due to its impressive mechanical,
thermal, optical and electronic properties, and the different possibilities of technological applications that these
exhibit systems. A special emphasis has been given the graphene nanoribbons (GNRs), since they exhibit interesting
electronic and magnetic properties. GNRs are classified according to the type of edges. There are two basic shapes
of edges, armchair and zigzag. GNRs present different electronic properties ranging from normal semiconductors
to spin-polarized half metals. Theoretically, various methods such as carrier injection, oxidation of two sides,
application of a magnetic field in the substrate, application of an in plane electric field, doping, hydrogenation
at the edges have been proposed to tune the magnetic and electronic properties. Another possible way to tune
these properties is to incorporate extended line defects (ELDs) in them. In this context, this paper proposes to
investigate how the inclusion of extended line defect 4 ELD (composed of four rings distorted tetragonal), 585 ELD
(formed by two pentagonal rings and an octagonal) and 48 ELD (consisting of a tetragonal and an octagonal ring)
modify the electronic and magnetic properties of graphene nanoribbons with zigzag edges (ZGNRs). For this we
use first-principles calculations based on density functional theory (DFT).
38
Effects of geometry and electric field in graphene ribbons conductance
Luan Vieira de Castro, João Milton Pereira Junior, Andrey Chaves
Graphene, a two-dimensional crystal made of carbon atoms, has attracted much interest in the last few years, due
to its unusual properties, such as a conical electronic dispersion with zero gap and an anomalous quantum-hall
effect. A graphene-based material which has also been intensively studied is the graphene nanoribbon (GN), i.e.
a flat strip of graphene. With GNs, it is possible to obtain nanostructures with electronic properties that are
distinct from those of pristine graphene. Thus, for GNs with armchair edges it is possible to open up a gap in the
electron spectrum, whereas for GNs with zigzag edges one can find localized edge states. Therefore, studying and
understanding the transmission properties of these ribbons and how they react to external perturbations can be
vital for future applications of graphene in devices.
In this work, we study the coherent transport of graphene ribbons with different geometries in the limit of zero
bias potential. We assume that the system is made of two parts: a central scattering region and two semi-infinite
leads attached to it, playing the role of electrodes. Linear response is assumed and the conductance is calculated
using the Landuaer-buttiker formula. We study how the size and the geometry of scattering region affect the
transmission of the system. We also apply a traversal electric field in the ribbon and we try to figured out how
that affects the charge transport.
39
Effects of oxygen vacancy in the electronic and optical properties of SnO2 slabs
B. Campos, I. Camps
In this work, we calculated the electronic and optical properties of tin dioxide slabs (SnO2 ) pure and with an oxygen
vacancy. This task was accomplished using first-principles calculations based on the Density Functional Theory
(DFT) as implemented in the SIESTA code. The slab structures were obtained from different crystallographic
planes from the tetragonal crystal of SnO2 (following experimental data from nanoribbons synthesized by goldcatalyst-assisted vapor-liquid-solid (VLS) method). Then, an oxygen was removed from the surface to create an
artificial vacancy. The study of the electronic properties of the structures was through the electronic band structure,
the total state density (DOS), the partial density of state (PDOS) and contour maps of the difference of electron
density. The optical properties such as absorption coefficient, refraction index and reflectance, among others,
were obtained from the calculated dielectric function. In all calculations, the Generalized Gradient Approximation
(GGA) following the parameterization of Perdew-Burke-Ernzerhof (PBE) was used. Before calculate the electronic
and optical properties, convergence studies for the grid cut-off energy and k-point sampling were carried on.
Our results shown that the oxygen vacancy has more effect in some planes affecting the electronic and optical
properties visible. In addition, depending on the crystallographic plane of the slab, the conduction mechanism
could be associated with a hopping mechanism. This is in accordance with recently experimental measurements
done in SnO2 nanoribbons. We acknowledge financial support of FAPEMIG.
40
Effects of atomic distribution on electronic properties of BxCyNz nanotubes
A.C.M. Carvalho, T.A. Souza
GDENB, Instituto de Fı́sica e Quı́mica - Universidade Federal de Itajubá, Avenida BPS 1303, Caixa Postal: 50 - CEP:
37500 903 - Itajubá - MG, Brazil
F. Sato
Departamento de Fı́sica - Instituto de Ciências Exatas - Universidade Federal de Juiz de Fora, Campus Universitário,
CEP 36036-900 - Juiz de Fora - MG, Brazil
M.S Ferreira
School of Physics, Trinity College Dublin, Dublin 2, Ireland
Tubular structures of boron nitride nanotubes (BNNT) were proposed theoretically in 1994 [1], due the structural
similarities between hexagonal boron nitride (h-BN) and graphene. Theoretical and experimental studies of other
tubular structures, such as boron carbonitride (BX CY NZ ) nanotubes, were motivated by the synthesis of BNNT
in 1995 [2]. Differently of carbon nanotubes, BNNT are always insulators with band gap energy of about 5.5 eV,
independently on their diameter and chirality. In the case of the B-C-N ternary tubular structures, theoretical
calculations have revealed that these nanotubes may manifest intermediate electronic properties between pure
carbon and boron nitride nanotubes. This characteristic means that BX CY NZ nanotubes could be useful in
technological applications for which carbon and BN nanotubes are unsuitable.
In this work, electronic properties of BX CY NZ nanotubes have been theoretically studied. Comparing the
results obtained via Density Functional Theory (BLYP/6-31G) and methods based on Greens function theory, we
concluded that the electronic properties of BX CY NZ nanotubes depend on the chemical composition and atomic
arrangement of B, C, and N atoms in the tubular structure.
This research is supported by Brazilian agencies: CNPq, CAPES and FAPEMIG.
[1] A. Rubio, J. Corkill, M. L. Cohen, Phys. Rev. B. 49 (1994) 5081-5084
[2] N. G. Chopra, R. J. Luyken, K. Cherrey, Science 269 (1995) 996-997
41
Influence of C and BN stripes on the electronic properties of BxCyNz nanotubes.
A.C.M. Carvalho, T. A. Souza
GDENB, Instituto de Fı́sica e Quı́mica - Universidade Federal de Itajubá, Avenida BPS 1303, Caixa Postal: 50 - CEP:
37500 903 - Itajubá - MG, Brazil
F. Sato
Departamento de Fı́sica - Instituto de Ciências Exatas - Universidade Federal de Juiz de Fora, Campus Universitário,
CEP 36036-900 - Juiz de Fora - MG, Brazil
Carbon nanotubes have attracted scientific and technological interest due to their extraordinary properties. Their
characteristics led researchers to investigate the possibility of others tubular compounds such as boron nitride.
Theoretical and experimental works have shown that carbon nanotubes can be either semimetallic or semiconducting, depending upon their structures. Otherwise BN nanotubes are caracterized by a wide band gap energy,
independent of radius and helicity. Since 1994, BX CY NZ nanotubes have been studied theoretically and experimentally [1]. Unlike pure carbon nanotubes, the eletronic structures of BX CY NZ nanotubes is predicted to be
ino uenced by their chemical composition, their geometrical structures and their atomic arrangement [2-4]. Calculations with first-principles density functional theory and semi-empirical calculations have suggested that the
electronic structures of BX CY NZ can be tuned simply by changing their atomic compositions and configurations.
This characteristic means that BX CY NZ nanotubes could be useful in technological application where carbon
and BN nanotubes are unsuitable. In this work semiempirical PM3 optimization and Density functional theory
(DFT) are done to investigate structural and electronic properties of these compounds. The boron and nitrogen
were incorpored as stripes wich are stacked in parallel and perpendiculary patterns along the nanotube axis. The
stoichiometries BCN, BC2 N , and BC4 N have been tested with several atomic distribution. Were analyzed the
changes in the electronic properties due to boron-nitrogen incorporation in carbon hexagonal network comparing
their density of states (DOS) result. We concluded that the band gap energy of BX CY NZ nanotubes depends on
chemical composition and atomic arrangement of B, C and N atoms in the tubular structures.
Acknowledgments: This work was supported by CAPES and FAPEMIG.
[1] Y. Miyamoto, A. Rubio, M. L. Cohen, and S. G. Louie, Chiral tubules of hexagonal BC2 N , Phys. Rev. B
50, (1994) 4976-4979.
[2] E. Zahedi, Size-dependent electronic structures of boron carbonitride (BC2N) nanotubes, A DFT approach,
Superlattices and Microstructures, Vol. 50, No. 5. (2011) 491-500.
[3] A. Freitas, S. Azevedo, M. Machado, J. R. Kaschny, First-principles calculations of BC4N nanostructures:
stability and electronic structure, Applied Physics A: Materials Science and Processing, Vol. 108, No. 1. (2012)
185-193.
[4] Y. Xie, H. Yu, H. Zhang, H. Fu, Tuning the band gaps and work functions via topology and carbon
concentration: a first-principles investigation of CX (BN )Y compounds, Chem. Phys, 4 (2012) 4391-4397.
42
First principles study of the electronic properties of GaSb/InAs core/shell nanowires.
Tanize Kohlhoff, Solange Binotto Fagan, Cláudia Lange dos Santos
Paulo Cesar Piquini
The growing techniques of semiconductors nanowires allow the synthesis of axially and radially modulated nanowire heterostructures. These nanostructures, due to the large surface to volume ratios, enable the integration of
mismatched material systems which cannot easily be combined in planar geometries. Furthermore, it is possible
to tune their electronic structures by the appropriate choice of their structural and composicional parameters.
Among these nanomaterials, nanowire heterostructures of group III-V semiconductors are interesting systems because of a structural similarity to silicon, narrow direct band gaps, and high carrier mobilities. Here, we use
first principles calculations to study the electronic properties of wurtzite [0001] and zinc-blende [111] GaSb/InAs
core/shell nanowires with different core/shell ratios. Our calculations were performed with the Vienna Ab initio
Package Simulation (VASP) within the Density Functional Theory. The Local Density Approximation was used
for the exchange-correlation potential and the electron-ion interactions were described by Projector Augmented
Wave method. Our results showed that for both, zinc-blende and wurtzite GaSb/InAs core/shell nanowires, the
band gap increases with increasing core/shell ratio. The electron states are localized in the shell region of the wire,
which corresponds to the InAs material, while the hole states are localized in the central region of the wire, which
corresponds to the GaSb core. These results are very interesting for the renewable energy applications, including
solar cells, where the spatial charge separation is desirable to reach longer recombination times. The valence band
offset and the conduction band offset are being analyzed.
43
Extrinsic and Intrinsic Defects in InN Nanowires from First Principles Calculations
Tomé Mauro Schmidt, Júlio César da Silva
Nitride semiconductors have potential applications in photodetectors and efficient solar cells. With the recent
discovery of small band gap 0.7 eV for InN, turn the nitride semiconductors to cover the entire solar spectrum.
More than that nanostructures of InN can be constructed with different band gap width, desired to different
technological applications. To dope InN is a hard task, mainly p-type system. In this work we investigate intrinsic
defects like N and In vacancies, as well extrinsic defects, using Mg impurity. We use a density functional theory
within the local and generalized gradient approximations to study the extrinsic and intrinsic defects in both bulk
and nanowire InN systems. Our results show that N vacancy and interstitial Mg in bulk InN present low formation
energy and they are n-type semiconductors. In vacancy and Mg substitutional at the In site are p-type systems,
but they present to high formation energies to be feasible. These results are in agreement with experiments, where
p-type bulk InN has been rare to obtain. On the other hand, for InN nanowires, the lowest formation energy defects
are Mg at In site, and interstitial Mg, which are p- and n-type systems, respectively. For the n-type interstitial Mg
the formation energy is a little smaller in the nanowire than in the bulk InN. However Mg at In site the formation
energy drops from 6 eV in the bulk to approximately zero in the nanowire. In this way InN nanowire can be easily
doped either n- or p-type system, making this nanostructured nitride promising for nanotechnological applications.
Our calculated InN nanowires present higher band gap than the bulk InN band gap. The projected density of states
show that the Mg defect level is inside the conduction band for the interstitial Mg, and it is inside the valence band
for the Mg at the In site. This picture for the electronic structure of n- and p-type InN nanowire, together to the
fact that InN present low effective mass, is expected to produce hight mobility nanodevices.
44
Electronic properties of the system CN T − (OH)x
M. S. Ribeiro, I. Camps
The aim of this work is to study the electronic properties of carbon nanotubes (CNT) functionalized with different
concentrations of the functional group -OH. The -OH group was added to the surface of the carbon nanotube
covering 0, 5, 10, 15 and 20 percent of its surfaces (these covering concentrations were selected due to steric
impediment when the concentrations are higher than 20%). The representative structures were selected after the
following procedure: (1) 10000 structures were generated for each concentration. The -OH groups were added
randomly to the carbon nanotube surface. (2) Following the ideas of quasi-random structures, using the USPEX
program, the quasi-entropy of each structure was calculated. (3) The structure with higher quasi-entropy was
selected. The electronic studied was carry out from the highest occupied molecular orbital (HOMO) and the
lowest unoccupied molecular orbital (LUMO) distribution and values; the electrostatic potential surfaces and the
molecular polarization. Using the Janak’ s theorem is possible to estimate the chemical potential (µ), the molecular
hardness (η) and the electrophilicity index (ω) from the HOMO and LUMO energies ϵH and ϵL , respectively, for
each representative structure. Our results shown a correlation between these properties and the functionalization
percentage. Knowing this relationship is very useful when designing nanostrutures as active zone of filters, sensors
and when using the functionalized carbon nanotubes mixed with other substances such as hydroxyapatites in order
to increase its mechanical properties. We acknowledge financial support of FAPEMIG.
45
Hydrogenation Induced Band Gap in Metallic Honeycomb Silicon Boron Monolayers
Anders Hansson, Fernando de Brito Mota, Roberto Rivelino
UFBA - BA - Brasil
The success of graphene has led to an extensive search for other monolayered structures. Particularly, structural
analogs of graphene, such as the insulating hexagonal boron nitride (h-BN), with essentially the same lattice parameters as graphene/graphite, and silicene, predicted to be a gapless semiconductor like graphene, have already
been fabricated. Recently, the authors[1] reported a two-dimensional (2D) BN-like structure of silicon and boron
(h-SiB), which was followed up by a proposal of structural variants of silicon boron monolayers by Dai et al. [2].
Different from most other known 2D structures, the silicon boron monolayers are all predicted to be metallic.
Except from remarkable conducting properties, tunable band gaps are highly desirable for applications in photonics and electronics. Therefore, several strategies to open band gap in these semimetallic monolayers have been
investigated. Absorption of hydrogen, is one appealing way which can open band gaps in both graphene[3] and
silicene[4]. In this work we investigate the effect of hydrogenation of h-SiB monolayers by means of first-principles
methods. We consider two ways of hydrogenation, on the boron sublattice and on the silicon sublattice, with a
hydrogen coverage of 25%, 50%, 75%, and, 100%, respectively. By utilizing the density functional theory with the
exchange and correlation functional approximated with the Perdew-Burke-Ernzerhof derivation of the generalized
gradient approximation as implemented in the siesta code, we optimize the geometries and examine the electronic
structures. For all the studied cases, hydrogenation on the boron sublattice is energetically favorable. Moreover,
siesta molecular dynamics simulations at room temperature show that the hydrogen atoms migrate from the
silicon to the boron sites within a few picoseconds. Regarding the electronic structure, all the included cases with
less then 100% hydrogenation remain metallic, while the applied method predicts a band gap around 0.8 eV for the
100% hydrogenation case. These results therefore indicate that hydrogenation can transform not only semimetallic
monolayers, such as graphene and silicene to semiconducting structures, but also intrinsically metallic silicon boron
monolayers and show an approach to tune the electronic properties of silicon boron monolayers by adsorption of
foreign chemical species. We gratefully acknowledge the FAPESB for financial support and the CENAPAD-SP for
providing computational facilities.
References
[1] Hansson, A. et al. Phys. Rev. B 86, 195416 (2012).
[2] Dai, J. et al. J. Phys. Chem. Lett. 4, 561 (2013).
[3] Zhou, C. et al. Nanoscale Res. Lett. 9, 26 (2014).
[4] Houssa, M. et al. Appl. Phys. Lett. 98, 223107 (2011).
46
Single or functionalized fullerenes interacting with heme group
Wallison Chaves Costa, Eduardo Moraes Diniz
The heme group is responsible for iron transportation through the bloodstream, where iron participates in redox
reactions, electron transfer, gases detection etc. The efficiency of such process can be reduced if the whole heme
molecule or even the iron is somehow altered from its original oxidation state, which can be caused by interactions
with nanoparticles as fullerenes. To verify how such particles alter the geometry and electronic structure of heme
molecule, here we report first principles calculations based on density functional theory using generalized gradient
approximation for the exchange-correlation potential of heme group interacting with single C60 fullerene or with
C60 functionalized with small radicals (−CH3 , −COOH, −NH2 , −OH). The calculations shown that no molecule
was able to move the iron from the heme molecule but there exist conformational modifications on heme geometry.
Also one find that heme molecule loses electrons to the nanoparticles and some systems exhibited a geometry
distortion in heme group. Also one find that such nanoparticles induce a formation of spin up states in heme
group. Moreover, there exist modifications in density of states near the Fermi energy. Although of such changes in
heme electronic structure and geometry, the iron atom remains in the heme group with the same oxidation state,
so that processes that involve the iron might not be affected, only those that depend on the whole heme molecule.
47
Magnetization Process in Arrays of Polycrystalline Ferromagnetic Nanowires
José Holanda da Silva Júnior, Eduardo Padrón Hernández
UFPE
In this work we produce an analytical model based on energy densities involved in the process of magnetization
reversal in coherent mode of arrays of polycrystalline ferromagnetic nanowires. We believe that our nanowires are
formed by ellipsoidal crystalline grains, as described in previous papers [1]. Based on the total free energy density
prevalent in nanowire arrays, we were able to study the magnetization process this system. For this, we constructed
an algorithm able to determine the angles of equilibrium magnetization through the expression of the total free
energy density and of the conditions for minimizing energy used by Stoner-Wohlfarth [2]. The results show that
the total free energy density can submit more than one minimum for the equilibrium position of the magnetization.
Furthermore, the fact that we have two minimum and one of them be a global minimum does not mean that the
magnetization is in this position. In fact, as we show what defines the equilibrium position of the magnetization is
the whole process of magnetic arrays. We construct another algorithm able to calculate the hysteresis loops using
the equilibrium conditions of the magnetization, the reduced field and the angle that we applied the external field.
We obtained hyteresis curves numerically for any angle of the applied field. Now we are studying the transport
properties of this type of system. [1] E. P. Hernández, S. M. Rezende and A. Azevedo. J. Appl. Phys. 103, 07D506
(2008).[2] E. C. Stoner and E. P. Wohlfarth, Philos. Trans. R. Soc. London, Ser. A 240, 599 (1948).
48
Diagrama de fases de materiais magnetocalóricos
Jardel Cardoso da Rosa, Ben Hur Bernhard
Universidade do Estado de Santa Catarina
O modelo da rede de Kondo é adotado para descrever uma variedade de materiais magnéticos contendo momentos
localizados e elétrons de condução. O diagrama de fases é obtido dentro de uma aproximação de campo médio,
incluindo as fases ferromagnética (FM) e antiferromagnética (AF), como função da interação de troca local JK e
da concentração eletrônica n. As magnetizações parciais são determinadas de maneira autoconsistente em função
da temperatura em presença de um campo magnético h. O diagrama h-T inclui as fases homogêneas FM e AF, e
uma fase PM a altas temperaturas. O efeito magnetocalórico (MCE) é caracterizado pela variação isotérmica da
temperatura ∆ST . Dando continuidade a estudos recentes, incluı́mos a presença da repulsão coulombiana local U
na banda de condução, investigando a sua influência nas transições de fase e no MCE.
[1] A.M. Tishin, Y.I. Spichkin, The Magnetocaloric Effect and its Applications, 1st edition, Institute of Physics,
Bristol, Philadelphia, 2003. [2]N.A. Oliveira, P.J. Von Ranke, Theoretical aspects of the magnetocaloric effect.
Physics Reports 489 (2010) 89159; [3] E. Brück; J.Phys. D: Appl. Phys. 38, R381 (2005); [4] A. O. Pecharsky, K.
A. Gschneidner, V. K. Pecharsky and C. E. Schindler, J. Alloys Compounds 338, 126 (2002); [5] D. Nascimento,
B.H. Bernhard, Solid State Commun. 167 (2013) 40; [6] F. Alfaro, B.H. Bernhard, Physica B 404 (2009) 3066; [7]
B.H. Bernhard, M.C. Siqueira, Solid State Commun. 149 (2009) 1777.
49
A Comparative Study of the Various Phases of FeSe1−x
L. Squillante, P. Menegasso, T. Gonçalves, F. dos Santos, M. de Souza
IGCE - Univ Estadual Paulista - Departamento de Fı́sica - Rio Claro (SP) - Brasil
L. Craco
Instituto de Fı́sica, Universidade federal do Mato Grosso, Cuiabá, Brasil
A. A. Haghighirad
Clarendon Laboratory, Parks Road, University of Oxford, Oxford, England
The discovery of superconducting materials containing iron in their structure consists one of the topics of high
interest in the field of condensed matter Physics research in the past few years. In this context, FeSe1−x is a binary
alloy material of particular interest due to its simple structure, which consists solely of Fe-containing (Fe2 Se2 )
layers. Interestingly enough, while its tetragonal phase (δ’ and β) shows superconductivity under ambient pressure
around Tc ∼ 8.5 K [1], the hexagonal phase (δ) does not superconduct. One of the issues still under discussion
in the literature is to find out the physical explanation for this exotic phenomenon. The synthesis of the FeSe1−x
samples investigated here was made employing the method of solid state reaction. High-purity iron (Fe) and selenium (Se) were mixed in an iron ampoule, being the synthesis performed using the appropriated parameters in
order to achieve the hexagonal phase (δ) of FeSe1−x [2]. Electrical resistivity measurements as a function of temperature show a semiconducting behavior in the temperature window 1.4 K < T < 300 K. In this contribution, a
detailed discussion of the transport properties [3, 4] of the δ, δ’ and β phases will be presented. Our findings will be
discussed in connection with the theoretical treatment based on the selective orbitals model of the 3d atoms of Fe [4].
This work was supported by the São Paulo Research Foundation (Fapesp) (Grants no 2011/22050-4) and National Research Council (CNPq) (Grants no 308977/2011-4).
[1] M. de Souza et al., The European Physical Journal B 77, 101-107 (2010).
[2] B. Massalski et al., Binary Alloy Phase Diagrams - Second Edition (1990).
[3] S. Medvedev et al., Nature Materials 8, 615 (2009).
[4] L. Craco, S. Leoni, Europhysics Letters 92, 67003 (2010).
50
Análise das Propriedades Eletrônicas e Magnéticas de Superfı́cies e Fitas de SiC
Larissa Sihe Oliveira, Rogério José Baierle
Laboratório de Estrutura Eletrônica dos Materiais - LEELMAT, Departamento de Fı́sica da Universidade Federal de Santa
Maria
Utilizamos simulações computacionais onde adotamos o método de primeiros princı́pios com base na Teoria do
Funcional Densidade (DFT). Os pseudopotenciais de norma conservada na sua forma totalmente separável serão
utilizados de modo a considerar a forte interação entre os elétrons de valência e os de caroço. Assim, resolvemos
as equações de Kohn-Sham de forma autoconsistente, onde a Aproximação do Gradiente Generalizado (GGA) nos
permite escrever uma aproximação para o termo de troca e correlação. A busca pela geometria é feita através do
algoritmo de Gradiente Conjugado (CG), com o cálculo de forças usando o procedimento de Hellmann-Feynmam.
Efetuaremos um estudo dos acerca das potenciais aplicações dos materiais semicondutores nanoestruturados, especificamente fitas de Sic na parte que envolve spin-trônica. O SiC é um material muito promissor por ser estável
quimicamente até altas temperaturas e pressões, possuir excelente condutividade térmica e biocompatibilidade.
Todos os cálculos serão realizados utilizando o código computacional SIESTA (Spanish Initiative for Electronic
Simulations with Thousands of Atoms). Após a realização das simulações, apresentaremos as estruturas de banda
correspondentes a cada um dos casos analisados. Apresentaremos os primeiros resultados obtidos com o SiC, que
dará inı́cio ao meu trabalho de mestrado a ser desenvolvido nos anos de 2014/2015. Posteriormente, este trabalho
deve ser estendido à estruturas mais complexas, como nanotubos puros, com vacância e dopados com N [3-4], a
fim de analisarmos suas propriedades e seu comportamento de semicondutor de gap nulo.
51
Ge doping of FeGa3
J C Alvarez-Quiceno, J M Osorio-Guillén, G M Dalpian
Universidade Federal do ABC - SP - Brasil
The intermetallic narrow-gap semiconductor compound FeGa3 is one of the few Fe based materials that is nonmagnetic. It has a tetragonal crystal structure with space group P42 /mnm and 16 atoms in the unit cell. The
Fe ion occupies the Wyckoff position 4f (u, u, 0), one type of Ga is located at the Wyckoff position 4c (0, 1/2, 0)
and another Ga occupies the Wickoff position 8j (u, u, w). Experimental data shows that doping FeGa3 with Ge
makes it become magnetic. There is currently a lot of discussion in the literature regarding the origin of this
magnetic behaviour. Ge is a donor when substituting Ga atoms. Consequently, an itinerant model for magnetism
is usually proposed. However, when FeGa3 is doped with Co, that is also a donor, no ferromagnetic behaviour is
observed, raising questions on the itinerant magnetism model. In order to understand this phenomenon better, we
have performed ab initio simulations for Ge-doped FeGa3 . For that we used the Density Functional Theory and
the PBEsol potential for the exchage-correlation term. We have studied Ge-doping concentrations of x =0.03125,
0.0625, 0.125, 0.1875, 0.25, 0.375, and 0.5, and observed that the system became ferromagnetic. In this poster we
will present detailed results on this material, trying to understand better the origin of ferromagnetism on it.
52
Electronic structure of Sr2 FeMoO6
H. P. Martins, R. J. O. Mossanek, M. Abbate
UFPR - Universidade Federal do Paraná, Departamento de Fı́sica
The Sr2 FeMoO6 material is a half-metallic ferromagnet with µ ≈ 4.0µB , and presents a low-field and hightemperature tunneling magnetoresistance (TMR) effect. Despite extensive studies, there are still open questions
about the electronic structure of this compound. In particular, what is the valence of the transition metal ions
and what is the role of the Mo 4d states. To this end, the electronic structure of Sr2 FeMoO6 was studied using
diverse experimental techniques. These techniques include X-ray photoemission (XPS), X-ray absorption (XAS)
and resonant photoemission spectroscopy (RPES). The experimental spectra were measured at room temperature
at the SXS and SGM beamlines in the LNLS (Campinas, Brazil). The experimental results were interpreted using
a cluster model, band structure, and atomic multiplet calculations. The valence of the transition metal ions in this
material could be: Fe2+ –Mo6+ , Fe3+ –Mo5+ , Fe4+ –Mo4+ , Fe5+ –Mo3+ and Fe6+ –Mo2+ . The analysis of the XAS
spectra shows that the transition metals in this oxide are in the mixed Fe3+ –Mo5+ valence state. The Fe 2p and
Mo 3p core level XPS spectra were used to determine the parameter set of the cluster model. The results indicate
a strong covalence between the oxygen and the transition metal states, and they also show the importance of the
Fe–O–Mo hybridization in this material. The cluster model with the same parameter set is able to reproduce the
main features in the valence band XPS spectrum. The RPES results show the existence of Mo 4d at the Fermi level,
as well as a strong hybridization with O 2p states at higher energies. These findings are important to understand
the electrical and magnetic properties of Sr2 FeMoO6 .
53
Electronic Structure of Sr2 TiRuO6
E. B. Guedes, M. Abbate, R. J. O. Mossanek
Universidade Federal do Paraná
Complex metal oxides have attracted considerable attention because of exotic properties at their interfaces as well
as in bulk phases. In particular, double perovskites of general formula A2 BB′ O6 are interesting from both applied
(low-field magnetoresistance and high TC ’s) and basic (phase transitions, correlation and covalence effects) points
of view. This class of materials shows a plethora of phases and phenomena that can be achieved by changing
the A cation or the B,B’ transition metals (TM). In this work, we focus on the electronic structure of the double
perovskite Sr2 RuTiO6 (SRTO). While SrTiO3 (STO) is a diamagnetic band insulator and SrRuO3 (SRO) is an
itinerant ferromagnet, the present material is a ferromagnetic insulator and presents unusual magnetoresistance
behavior. Previously, a single cluster model was used to study SRO and other perovskites by our group. That
model considered a TMO6 octahedron and took into account covalence, correlation and multiplet effects. Now, in
order to study the electronic structure of SRTO, we developed a double cluster model, in which two octahedra are
connected via an oxygen atom, so that the B–O–B′ interaction is included. We also performed atomic multiplet
calculations to further confirm valence state of Ti ions in the compound. The results from both approaches are
compared with X-ray Photoemission Spectroscopy and X-ray Absorption Spectroscopy measurements from the
literature, and all the spectra were reproduced with a single set of parameters.
54
Electronic properties of graphene nanoribbons containing structural defects.
Fabrı́cio Morais de Vasconcelos, Eduardo Costa Girão
UNIVERSIDADE FEDERAL DO PIAUI
Even though the study of planar carbon nanostructures (where carbon atoms undergo sp2 hybridization) has been
carried on for more than a decade, a greater attention has been devoted to them since the first isolation of a
graphene sheet by Geim and Novoselov in 2004 [1]. Since then, the current of though which believes that carbon based materials will substitute silicon as the basis material for electronics has gained more and more force.
This is due to the huge set of singular properties these marterials show, as revealed by an increasing number of
theoretical and experimental investigations [2]. While the carbon nanostructures family is very broad, graphene
plays a special role on it due to interesting physical properties such as high mobility and low contact resistance.
However, several application in nanoeletronics need a material with an electronic band gap and graphene is not
a semiconductor at room temperature. Among the various strategies to modify graphene’s properties in order to
open a band gap, the production of graphene like systems which are finite in one direction (so as to form the so
called graphene nanoribbons - GNRs) is a possibility widely studied on the literature. In this work we study the
electronic properties of GNRs with structural reconstructions along the ribbon’s periodic direction. Here we use a
Tight-Binding model including a Hubbard Hamiltonian to capture the different magnetic states present on systems
with a zigzag configuration for the atoms along their edges. We investigate how the system’s electronic properties
behave as we vary the details of the atomic structure of the extended line of defects both at the edges and in the
interior of the GNRs. We point out that these defects can offer a particular way to tune the electronic properties
of GNRs, so that once inserted in a broader library of structures, they can enable the development of a new class
of electronic and/or spintronic devices at the nanoscale.
[1] K. Novoselov, A. Geim, S. Morozov, D. Jiang, Y. Zhang, S. Dubonos, I. Grigorieva and A. Firsov. “Electric
field effect in atomically thin carbon films”. Science 306(5696), 666 (2004). [2] R. Van Noorden, Nature 469, 14
(2011).
55
Electronic and transport properties in carbon nanostructures with edges of complex geometry
Dayvison Weber Maia, Eduardo Costa Girão
Carbon nanostructures presenting sp2 hybridization, like graphene, are considered as good candidates to substitute
Silicon as the basis material for the production of smaller and more efficient electronic devices with the goal of
reaching nanoscale [1]. While graphene is not a semiconductor at room termperature (what is needed for specific
applications in nanoelectronics), it can undergo physical or chemical modifications in order to open such a gap.
Graphene-like structures which are finite in one dimension are a proposal intensively studied in the literature.
These are the so-called Graphene Nanoribbons (GNRs) [2,3]. In this work we apply computational simulations
to study the electronic and transport properties of graphitic ribbons which are based on a more complex ribbon
structure (called GNW - Graphene Nanowiggles) recently studied in the literature [4,5]. In our work we consider
a variation of this last structure which is similar to two GNWs joined along their non periodic direction, what we
called RGNWs (Reflected Graphene Nanowiggles). The simulations used to investigate these ribbons are based on
a Tight-Binding approach together with a Hubbard Hamiltonian (electronic structure) as well as in the Landauer
formalism combined with Green’s functions (electronic transport), which were previously applied to study similar
systems [5,6]. We find out that these structures present multiple geometric domains (finite zigzag edge sectors)
which give rise to several non-trivial configurations for the polarization of the electronic spin, resulting in different
electronic and transport properties for each of these magnetic states. We show that the spin distribution can be
used to tune the electronic properties of these RGNWs in strategic ways, so that these systems can be potentially
used as prototypes for new nanoelectronic and/or spintronic devices.
[1] R. Van Noorden, Nature 469, 14 (2011).
[2] Pisani et al., Physical Review B 75, 064418 (2007).
[3] Son et al., Physical Review Letters 97, 216803 (2006) .
[4] J. Cai et al., Nature 466, 470 (2010).
[5] E. C. Girão et al., Physical Review Letters 107, 135501 (2011).
[6] R. Landauer, Journal of Physics-Condensed Matter 1(43), 8099 (1989).
56
Organic molecules deposited on graphene
Igor Saulo Santos de Oliveira, Roberto Hiroki Miwa
Universidade Federal de Uberlândia (UFU)
In recent years, carbon-based two-dimensional nanostructures have been extensively investigated due to their
strong technological appealing in the development of new nanoelectronic devices, and also as a good platform
to investigate new physical phenomena in low dimensionality systems. In particular, graphene has attracted wide
attention since its discovery [1], due to its unique structure and properties it shows numerous potential applications
in nanoelectronic devices. The deposition of organic molecules on graphene can modify its physical properties, both
for molecules and substrate [2]. The molecules may work as a donor or acceptor of electrons to/from graphene, this
behavior can be tailored to adjust the graphene properties for electronic applications. It has also been observed
the self-assembly of molecules deposited on graphene [3]. In this work we investigate the deposition of TCNQ,
F4-TCNQ and TPA molecules on graphene pristine and presenting extended defects. We use computer simulations,
based on the Density Functional Theory, to study the stability and electronic structure of molecule(s)/graphene
systems. We show that all three molecules can form self-assembled structures on graphene. We also observed a
transference of electrons from the graphene carbon atoms to the TCNQ and F4-TCNQ molecules, while there is
no charge transfer to the TPA molecules. The application of an external electric field increased or decreased the
charge transfer, depending on its signal.
[1] K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva and A.
A. Firsov. Science 306, 666 (2004).
[2] Guo Hong, Qi-Hui Wu, Jianguo Rena, Chundong Wang, Wenjun Zhang and Shuit-Tong. Nano Today 8,
388 (2013).
[3] E. C. H. Sykes, Nature Chemistry 1, 175 (2009).
57
THE NANOCRYSTALLINE APATITES IN BONE MINERAL: CONCEPTS IN THE
COMPOSITION
Rafael dos Santos Geonmonond, Mirta Mir
Instituto de Ciências Exatas - ICEx, Universidade Federal de Alfenas - UNIFAL-MG.
The bone mineral is composed of non-stoichiometric nanocrystalline apatites, Ca10−x (P O4 )6−x (HP O4 , CO3 )x (OH; F ; ...)2−
where 0 < x < 2. One of the specificities of the apatite structure is its ability to accommodate many types of ions
as well as large amounts of vacancies. For the fabrication of materials to be incorporated into the bone structure,
the ideal is that they present structure and properties similar to bone presenting a high biocompatibility and
bioactivity. Nanocrystalline apatites play an important role in biomineralization and they are used as bioactive
materials for orthopedics applications. Several routes leading to different apatite compositions are found in biological systems. Hydroxyapatite is an example of mineral widely used for this purpose, which can be synthesized by
various routes to get the material with specific properties, such as bone grafts and dental implants. The properties
of nanocrystals appear to be strongly dependent on the composition (ions) and on the amount of vacancies present
in the structure. In this specific case, if a carbonate ion is substituting for a phosphate ion, there has to be a
reduction in the number of calcium ions to maintain charge balance besides generating vacancies in the structure.
The substitution sites of carbonate ions in the apatites structure have been classified into three types: type A
substitutes the OH site (named type A carbonate apatite), type B for the P O4 site, and type AB for both OH
and P O4 sites.
In this study, nanocrystalline apatites samples [Ca10−x (P O4 )6−x (CO3 )x (OH)2−x ], were obtained for different
compositions (0 < x < 2). The results suggest that for samples with 0 < x < 0.92 type B structure can be
obtained, and for large values of x generally is formed structure type AB. The study was based on analysis of
four theoretical models of composition to obtain a theoretical model that best represents our experimental data.
The results suggest that the amount of CO3 introduced into the sample, influences the crystallinity and site would
occupy in the structure. The reactivity of the apatite nanocrystals can play a part in different biomaterials and
could explain the setting reactions of biomimetic calcium phosphate cements and the possibility of obtaining a
material similar to bone in composition and crystallinity. This paper is aimed at illustrating some of the numerous
potentialities of calcium phosphate apatites in the bio-medical field, allowing one to foresee perspectives lying well
beyond bone-related applications.
We acknowledge financial support of FAPEMIG
58
Klein Tunneling through a time dependent potential barrier
G. O. Sousa, A. Chaves, J. M. P. Junior, G. A. Farias
UFC - CE - Brasil
The effect known as Klein tunneling, where relativistic particles have a high probability of tunneling through
potential barriers, has returned to attract interest in recent years, especially after the first experimental realization
of graphene in 2004. This is due to the fact that graphene, a two-dimensional material composed by bounded
carbon atoms arranged in a honeycomb structure, presents an almost linear dispersion for low energy electrons, so
that these electrons can be viewed as massless Dirac fermions, thus undergoing this tunneling effect, which hinders
the use of grafene in electronic devices. It then becomes important to study the Klein tunneling in detail in order
to understand, prevent, or even to take advantage of the inherent characteristics of this effect.
In this work, we studied how a wave packet describing a massless Dirac fermion, representing a low-energy
electron in graphene, behaves when it collides with a time dependent potential barrier. We investigate how energy
and probability density of this package changes when going through such a barrier. For this purpose, we use the
Split-Operator method, which allows us to separately apply the terms due the potential and kinetic energies in the
time evolution operator. With this, the kinetic energy part is solved analytically, while the potential energy part
is applied to the wave function in a trivial way. Our results show that wave packet undergoing Klein tunneling
through the potential barrier acquires an additional phase that, in our case, depends on time. Thus, considering a
wave packet scattering on a barrier which depends linearly on time, it is shown that this phase eventually changes
the final energy of the wave packet. This enables us to control the energy of the electron that propagates in
graphene by simply adjusting the width and rate of change of potential in time.
59
Um estudo teórico do campo interior em semicondutores extrı́nsecos
Giovanne de Sousa Monteiro, Miguel Lourenço Neto
IF SERTÃO - PE
Rodrigo José da Silva Lima
Certbio/Unidade Acadêmica de Fı́sica - UNIVERSIDADE FEDERAL DE CAMPINA GRANDE
Kennedy Leite Agra
UNIVERSIDADE FEDERAL DO RIO GRANDE DO NORTE
Os semicondutores são substâncias com resistividade entre a de um condutor e a de um isolante, e que pode variar segundo as condições fı́sicas a que está submetida, sendo particularmente sensı́vel à temperatura. Um cristal
semicondutor pode ser extremamente puro, sendo chamado de semicondutor extrı́nseco. Nesse trabalho, consideraremos um semicondutor extrı́nseco, de comprimento finito na direção - x, que é dopado com uma concentração
de impurezas eletricamente ativas, sendo concentrações de impurezas aceitadoras e doadoras, e são independentes
de y e z. Suponhamos que este semicondutor extrı́nseco esteja ligado a um potencial externo V(x), e que possui
dimensões suficientemente grandes nas direções y e z, e ainda, que todas as propriedades fı́sicas dependerão somente
de x e podemos estuda-lo como objetivo unidimensional. Consideramos o problema de achar o potencial interior
neste semicondutor extrı́nseco para uma dada concentração de transportadores, ou seja, elétrons e buracos. Para
simplificar o problema suporemos que se pode desprezar a recombinação e a geração de transportadores. Sob certas
condições podemos supor que o sistema de elétrons e buracos é um sistema clássico. Então as concentrações de
equilı́brio de elétrons e buracos num campo potencial interior são dados pela estatı́stica de Maxwell-Boltzmann.
Supondo válidas todas as condições expostas, o potencial interior é dado como solução da equação de Poisson.
60
Caracterização da elbaı́ta gemológica por espectroscopia UV - visı́vel e DRX
Miguel Lourenço Neto, Giovanne de Sousa Monteiro
IF SERTÃO - PE
Dwight Rodrigues Soares, Ana Cláudia Mousinho Ferreira
IFPB - campus Campina Grande
Hartmut Beurlen
UFPE - Departamento de Geologia
José Suassuna Filho
Unidade Acadêmica de Fı́sica, UFCG
A identificação e caracterização de centros de cor em espécies minerais, tem sido recentemente realizadas utilizando
técnicas espectroscópicas mais diversas. E sabido que ı́ons de metais de transição tais como cátion Fe3+, Fe2+,
Cr3+, Mn3+, Mn2+ e Cu2+, Ti4+ isolados ou em combinações, são os responsáveis pela origem da cor em
muitos minerais, notadamente em pedras preciosas. A elbaita azul desse estudo é proveniente do pegmatito Alto
Serra Branca localizado em Pedra Lavrada, Paraı́ba, Provı́ncia Pegmatı́tica da Borborema (PPB). Essas elbaı́tas
apresentam-se sob a forma de cristais idiomórficos de cor azul safira, com estrias e fratura conchoidal caracterı́sticas,
dureza variando entre 7 e 7,5, densidade de 3,12 g/cm3, ı́ndice de refração variando entre
varepsilon = 1,620, e w = 1,640 com birrefringência de 0,020. As amostras dessas elbaı́tas foram inicialmente
caracterizadas por espectroscopia UV-Visı́vel. O espectro de absorção UV-Visı́vel da elbaı́ta azul do pegmatito
Serra Branca, obtido para faixa de 190 a 1100 nm, exibe duas intensas bandas centradas em aproximadamente
725 e 1100 nm, provavelmente atribuı́das à presença de Fe2+. Um pico centrado em aproximadamente 230 nm
é atribuı́do a possı́vel transição associada ao mecanismo de transição de valência intermediária via transferência
de cargas (IVCT) do par (O2- - Fe2+). Estudos a partir de difração de raios X DRX e de refinamento Rietveld
encontram-se em andamento.
61
Computational Design of silica mesostructures for carbon capture and storage: Controlling
confined fluids
Yuri Menzl Celaschi, James Moraes Almeida, Lucas Stori de Lara, Caetano Rodrigues Miranda
UFABC
We have studied the effects of confined CO2 in mesoporous silica structures. Four channels with different diameters
(1, 2, 3, 4 nm) have been computationally modeled using an amorphous silica matrix. The channels were created
using an own code based on the Monte Carlo method with Metropolis algorithm. In order to describe different
degrees of hydrophilicity of the surface, this code allows us to create different chemical environments onto to the
surface of the channels by generating different ratios of terminations SiOH, Si(OH)2 and Si(OH)3. The structural,
thermodynamic and transport properties of confined CO2 in the silica pores were studied using classical molecular
dynamics. The interactions between atoms were described by applying the EPM-force field for CO2 and the CruzChu one to mesostructure. The mixing potential rules by Lorentz-Berthelot has been used. The pressure was
varied between 50 and 200 atm, keeping the temperature constant at 300K. Variations of SiOH terminations were
13
62
IDENTIFICAÇÃO DE BIOMOLÉCULAS FUNCIONAIS DO GRUPO DOS POLIFENÓIS EM
FRUTAS E VEGETAIS POR ESPECTROSCOPIA FOTOACÚSTICA
Fausto Vaz de Oliveira 1 , Aline Simões dos Santos 1 , Miguel Lourenço Neto 2 , Kennedy Leite Agra 3 , Rodrigo José da
Silva Lima 1.4 , José Suassuna Filho 1 , Giovanne de Sousa Monteiro 2
1- Unidade Acadêmica de Fı́sica, UFCG 2- IF Sertão Pernambucano - campus Petrolina 3- Departamento de Fı́sica,
UFRN 4- CERTBIO/UFCG - Lab. de Desenvolvimento e Avaliação de Biomateriais do Nordeste
Neste trabalho usamos a técnica de Espectroscopia Fotoacústica na identificação de Biomoléculas Funcionais,
presentes em várias frutas e vegetais. Essas biomoléculas, em geral compostos polifenólicos, formam grupos de
substâncias amplamente distribuı́dos em plantas, frutas e legumes, componentes comuns da alimentação humana,
especialmente flavonóides e taninos que possuem diversas propriedades terapêuticas e farmacológicas. Dentre as
espécies de frutas e cereais investigadas, cientificamente estabelecidas como depositárias de moléculas bioativas,
algumas se destacam por suas excelentes propriedades funcionais, tendo, por este motivo, recebido o nome pomposo
de “superfrutas”. São elas caracterizadas por apresentarem altas concentrações de polifenóis tais como as antocianinas, os flavonóis (quercetinas, kaempferol, catequinas, resveratrol e taninos), os ácidos fenólicos como o gálico,
o ascórbico, o elágico, o clorogênico, o benzóico, o felúrico, etc e os carotenóides, onde se destacam o β -caroteno,
licopeno, violaxantina, zeaxantina, luteı́na, neoaxantina, dentre outras. As superfrutas são assim classificadas
por exibirem extraordinário valor funcional. Os resultados experimentais obtidos por espectroscopia fotoacústica
para os comprimentos de onda λmax que representa os picos de absorção em cada amostra de frutas e vegetais
investigados evidenciam a existência de Biomoléculas Funcionais, que fazem bem a saúde humana. Nossos resultados, obtidos pela técnica de Espectroscopia Fotoacústica, confirmam esta como uma ferramenta experimental de
grande potencial e eficiência na identificação de biomoléculas em sistemas biológicos “in natura”, sem necessidade
de utilização de processos exaustivos de extração molecular.
63
Adhesion of hydroxylated α-quartz silica surfaces through a water monolayer.
James M. de Almeida, Caetano Rodrigues Miranda, Wanderlã L. Scopel, Antônio J. R. da Silva, Adalberto Fazzio
UFABC, UFABC, UFES, LNLS, USP
We have modeled the confinement of a water monolayer between two hydroxylated silica α-quartz surfaces. The
methodology employed was Density Functional Theory (DFT) with and without van der Waals corrections (vdW),
with PW91 exchange-correlation functional. The optimum number of water molecules between the two surfaces
([0001] direction) was found to be one per each 18.82 Å2 . No significant charge transfer was observed between
the silica surfaces and the water molecules, just a charge redistribution. For the optimised water concentration,
energetics, mechanical and electronical properties were determined. A higher number of hydrogen bonds (HBs),
and lower HBs angles were observed when vdW corrections were applied. When the surface separation is increased,
the HBs start to breakup. However, when there is such rupture, the remaining HBs get an increase in the angle and
decrease in the bond length, thus leading to stronger HBs. The Young’s modulus, perpendicular to the surfaces
(water layer) has been determined. The obtained values were: without (with) vdW corrections 35% (38%) of the
bulk silica α-quartz Young’s modulus. Remarkable, the structure with a water layer maintains much of its stiffness.
As many colloidal materials depends on the interactions of small areas of water-wet surfaces, this kind of stiffness
could sustain these materials.
64
Current density at puddles interfaces in graphene nanoribbons
Leandro R. F. Lima, Caio H. Lewenkopf
Graphene is an exciting material with a variety of interesting properties [1]. One of its several impressive properties
is the typical conductivity minimum of about e2 /h, almost independent of sample mobility, at the charge neutrality
point. This is at odds with the notion that as the mobility increases, and graphene becomes more ballistic, its density
of states (DOS) and conductivity at the charge neutrality point should vanish. The observed conductivity minimum
is often attributed to the presence of electron-hole charge puddles [1,2], which where confirmed experimentally [3],
that give rise to an effective local-dependent chemical potential. In this way, the local chemical potential fluctuates
creating p and n-doped regions and the electronic transport is facilitated by Klein tunneling through the p and
n-doped domains. Although very appealing, there is little quantitative support for this this picture. We revisit this
problem and analyze the transport properties using a self-consistent recursive Green’s functions technique [4] with
spin resolution that includes the electronic interaction through a mean field Hubbard term. We calculate electronic
current densities between neighboring carbon sites near the p-n interface and relate the electronic propagation to
the puddles charge, size and shapes.
[1]
[2]
[3]
[4]
A. H. Castro Neto et al, Rev. Mod. Phys. 81, 109 (2009).
M. Katsnelson, Graphene: Carbon in Two Dimensions (Cambridge University Press, 2012).
J. Martin et al, Nature Physics 4, 144 (2007).
C. H. Lewenkopf and E. R. Mucciolo, J. Comput. Electron. 12, 203 (2013).
65
N-rich B-C-N layers: from segregated alloy to solid solution
Jonathan da Rocha Martins
Hélio Chacham
Universidade Federal do Minas Gerais
Boron-carbon-nitrogen (B-C-N) layered materials such as graphene-type single layers, multilayers, and nanotubes
show electronic and transport properties that range from those of the large-gap insulating boron nitride to those of
the semimetallic or small-gap carbon nanostructures, depending on the B-C-N chemical composition. The degree
and type of B-C-N alloying in these materials also depend on chemical composition. For instance, near the B/N=1
ratio, the materials show segregation into either graphene islands in a planar BN matrix or BN islands in a graphene
matrix, depending on the C/BN ratio. This is consistent with theoretical simulations. In contrast, in N-rich B-C-N
materials there are indications that the carbon atoms are diluted in the BN matrix. The optical and transport
properties are also strongly dependent not only on the C content, but also on the B/N ratio. In the present
work we combine the Monte Carlo simulated annealing and density functional methods to investigate the effect
of composition on structural and electronic properties of Bx Cy Nz alloys organized on a honeycomb lattice. We
perform a theoretical study of nitrogen-rich B-C-N graphene-type alloys through a combination of Monte Carlo and
ab initio methods. Different from the B/N = 1 limit, where both calculations and experiments indicate segregation
into BN and C regions, the simulations of the N-rich alloys result in solid solution materials, with isolated carbon
substituting boron sites of BN. We show that this is a consequence of the competition between bond energies. As
a result of the solid solution morphology, the electronic structure of N-rich alloys depict a ≈ 1.5 eV wide, half filled
carbon impurity band that would result in either metallic behavior or disorder-induced semiconducting behavior
with a mobility gap.
66
Gaussian deformations in graphene ribbons: flowers and confinement
Ramon Carrillo-Bastos
Ohio University, Centro de Investigación Cientı́fica y Educación Superior de Ensenada, UNAM
Daiara Faria, Andrea Latgé
Francisco Mireles
Centro de Investigación Cientı́fica y Educación Superior de Ensenada
Nancy Sandler
Ohio University
Graphene nanoribbons (GNR) display the exceptional properties predicted for electronic transport in graphene.
Narrow strips of the material have been produced by methods such as lithography, unzipping of carbon nanotubes,
and chemical techniques. In particular, deposition on patterned SiC substrates produces ribbons with unusual large
conductivities, suggesting a strong connection between strain and conductance [1]. Effects of strain on electronic
properties have also been reported in graphene nanobubbles, drumheads and oscillating membranes [2] among
others. To investigate strain signatures, we focus on GNR with centro-symmetric out of plane deformations. A
tight-binding model is solved with the recursive Greens function method, to obtain conductance and local density of
states (LDOS). Results are compared with a Dirac model solved by iterative scattering matrix methods. We observe
an enhancement of the density of states in the deformed region, accompanied with a decrease in the conductance,
signaling the presence of confined states [3]. The local density of states exhibits a six-fold symmetric structure with
an oscillating sub-lattice occupation asymmetry, that persist for a wide range of energy and model parameters.
[1] J. Baringhaus, et al. Nature (2014) doi:10.1038.
[2] N. Levy, et al. Science 329, 544 (2010). T. Mashoff, et al. Nano Lett. 10, 461 (2010). N. Klimov, et al.
Science 336, 1557 (2012).
[3] Carrillo-Bastos et al. arXiv:1405.1962.
67
Fano resonances in hexagonal zigzag graphene rings under external magnetic flux
Daiara Faria, Andrea Latgé
Ramon Carrillo-Bastos
Ohio University, Centro de Investigación Cientı́fica y Educación Superior de Ensenada, UNAM
Nancy Sandler
Ohio University
Among graphene based systems, closed ring geometries have been extensively studied, with specific predictions of
energy spectra and conductance oscillations [1]. Very recently, experimental synthesis of graphene rings have been
successfully achieved, rendering rings with hexagonal symmetry caused by lattice orientation[2]. These new devices
present the opportunity to test these predictions and reveal yet unstudied new phenomena, as the rings are opened
to reservoirs.
We present results of a model for a graphene hexagonal quantum ring connected to semi-infinite zigzag nanoribbons, named as HZGQRs-GNRs. The total and local density of states, conductance and current density results are
obtained following the tight-binding approximation in the Green’s function formalism. We show that the coupling
of hexagonal rings to metallic contacts results in localized states due to the different geometries of the ring and of
the leads. While these states do not contribute to conductance, the presence of an external magnetic flux makes
possible the mixing of such states with the continuum background. In other words, the magnetic fluxes change the
nature of the bound states generating Fano resonances in the conductance at specific energy values that exhibit
an oscillatory dependence on the applied flux. Transmission experiments, therefore, would be able to probe this
resonant behavior. We also explore the effect of an out- of-plane deformation[3] on the electronic properties of the
open ring and we show that the Fano resonance profile can be even used to estimate the strain strength without
the need of local probes.
[1] J. Schelter et al., Solid State Comm.152, 1411 (2012). D. A. Bahamon et al., PRB 79, 125414 (2009).
[2] J. Baringhaus et al., Nature 506, 349 (2014).
[3] D. Faria et al., PRB 87, 241403(R) (2013).
68
Caracterização da gahnita gemológica por espectroscopia UV-visı́vel, EDS e DRX
Miguel Lourenço Neto, Giovanne de Sousa Monteiro
IF SERTÃO - PE
Dwight Rodrigues Soares, Ana Cláudia Mousinho Ferreira
IFPB - campus Campina Grande
José Suassuna Filho
Unidade Acadêmica de Fı́sica, UFCG
Ranjana Yadav
UFPE - Departamento de Geologia
Gahnita é um mineral do grupo dos espinélios (AB2 O4 ), onde os sı́tios estruturais A e B são dominados respectivamente por Zn e Al, com considerável substituição de Zn por F e e M g, e com provável solução sólida completa entre
ZnAl2 O4 e M gAl2 O4 . Gahnita não é uma fase mineral de ocorrência abundante em pegmatitos granı́ticos e quando
apresenta qualidade gemológica torna-se rara. Na Provı́ncia Pegmatı́tica da Borborema (PPB) a gahnita ocorre em
vários pegmatitos, entre eles, Quintos, Alto Mirador, Capoeira, e Carrascão. A gahnita do pegmatito Alto Mirador,
Carnaúba dos Dantas/RN, estudada nesse trabalho, ocorre nas cores verde clara e verde escura. A composição
quı́mica média das gahnitas a partir de análises de EDS (Espectroscopia de Energia Dispersiva) via microssonda
eletrônica, calculada para 32 oxigênios e com conteúdo de F e2+ e F e3+ , estimado pelo método de Droop são: gahnita
B
verde clara- A (Zn7,51 F e2+
0,14 M n0,19 M g0,057 Ca0,002 )7,90 (Al16,06 Si0,004 T i0,003 Cr0,001 )16,06 O32 ; gahnita verde escura2+
A
B
(Zn6,98 F e0,38 M n0,21 M g0,44 Ca0,001 )8,007 (Al15,95 F e3+
0,037 Si0,004 T i0,002 Cr0,001 )15,99 O32 . É importante observar que
o F e3+ não aparece na composição quı́mica da gahnita verde clara, pois é muito baixo, estando no limite de detecção
da microssonda eletrônica. Amostras de gahnitas foram submetidas à espectroscopia de UV-Visı́vel no Laboratório
de Fotoacústica da Unidade Acadêmica de Fı́sica da UFCG, com obtenção de 3 espectros (dois para verde claro
e um para gahnita verde escura) . O espectro de absorção UV-Visı́vel das gahnitas verdes obtido para faixa de
190 a 1100nm, exibe bandas centradas em aproximadamente 370, 430, 510, 660nm. Estas bandas são atribuı́das
à presença tı́pica de F e3+ em sı́tios octaedrais, indicando uma substituição do alumı́nio por ferro. Um estudo do
campo cristalino encontra-se em andamento para uma total elucidação do espectro UV-Visı́vel desse mineral. Os
espectros mostram picos nas mesmas posições, mas com intensidades diferentes. Estão em andamento as análises
dos resultados de difração de raios X (DRX) e de refinamento Rietveld.
69
The influence of the C stripes in the structure, energetics and eletronic properties of BN nanotubes
Sérgio Azevedo
Fernando Mota, Jemima Pereira
Universidade Federal da Bahia
Carbon and boron nitride nanotubes present significant differences in their electronic properties. However, they
have isoelectronic bonds and very similar geometrical structures that allow BCN nanotubes to be synthesized and,
for this reason, have attracted recent interest in the literature due to their novel structural, optical, and electronic
properties. These materials, first synthesized in the mid- 1990s , have band gaps and other electronic properties
that are intermediate between those of pure carbon and BN. Moreover, these BCN nanotubes present properties
that can vary according to their relative number of B,C, and N atomic distribution on the nanotube surface.
Recent experimental results on BCN nanotubes confirm that segregation in pure C and BN phases is energetically preferable, as previously predicted by theoretical works. Some researchers considered BC2 N structures with
alternating ribbon regions of carbon and BN. They showed that the larger the width of the pure ribbons, the lower
is the energy, indicating a strong tendency for C/BN segregation. They also found that the band gaps decrease
with increasing ribbon widths.
Motivated by these recent experimental and theoretical results on hybrid nanostructures of C and BN we study
theoretically by Density Functional Theory (DFT), as implemented on the SIESTA code, mainly the defects like
single-, double- and multiple-line of C on BN nanotubes. Weve found that the presence of these defects causes a
semiconductor character to those nanotubes as the band-gap was reduced from 4.4 eV down to 0.20 eV, depending
on the number and arrange of these linear defects on the tube. In this sense, our study clearly presents a variety
of electronic states, opening the possibility of a tunned band-gap, one of the hottest topics of the real scenario.
This results may also suggest potential tracks for hybrid-nanomaterial engineering for advanced materials and
applications.
This project is supported by CAPES
70
Stability and optical properties of hybrid nanostructures
Sergio Azevedo
The structural similarity between graphite and hexagonal BN motivated the synthesis of alloys of these materials.
One expects that the conduction and intercalation properties of such hybrids could be intermediate between these
of semi-metallic graphite and insulating BN. Hence, BxNyCz compounds are of potential technological interest.
Unfortunately, B-C-N honeycomb nanostructures are much harder to synthesize than their carbon counterparts,
with few experimental studies. However, recent results may provide solutions to this problem. In a recent paper
[1] has reported the synthesis and characterization of large-area atomic layers of h-BNC materials, consisting of
hybridized, randomly distributed domains of h-BN and C phases with compositions ranging from BN pure to pure
graphene. In this contribution we have applied first-principles calculations to perform a detailed study of the
energetic and electronic properties of Bx NyCz hybrid bilayers. It is considered structures composed by a graphene
monolayers including a BxNy nanodomains with different size and B-N concentrations ratios. It is shown that
the stability and optical properties of C bilayers are strongly affected by the introduction of BxNy domains. It is
possible to verify that the careful control of the size of BN nanodomains in carbon bilayers can lead to the synthesis
of nanomaterials with tunable energy gap.
Referências
[1] Lijie Ci, Li Song, Chuanhong Jin, Deep Jariwala, Dangxin Wu, Yongjie Li, Anchal Srivastava, Z. F. Wang,
Kevin Storr, Luis Balicas, Feng Liu and Pulickel M. Ajayan, Nature Materials 9 (2010) 430.
71
Potential Energy Surface for the BeGe molecule.
Robson A. Simões, Vladir W. Ribas
Laboratório Associado de Plasma - LAP, Instituto Nacional de Pesquisas Espaciais - INPE/MCT, São José dos Campos,
SP, CEP 12247-970, CP515, Brazil.
In this work we are concerned with a description of the Potential Energy Surface (PES) for the twenty low-lying
singlet and triplet electronic states of the BeGe molecule. These states correlate with the three lowest dissociation
channels. The first two states (X)3 Σ− and (1)3 Π correlating with the first dissociation channel, Be (1 Sg) + Ge
(3 P g), and the four states 1 Π(1), 1 Σ+ (2) and 1 ∆(1) correlating with the second and third channels, Be (1 Sg) +
Ge (1 Dg) and Be (1 Sg) + Ge (1 Sg), respectively. The electronic calculations basically involved two steps. The
first step consisted of state-averaged complete active space self-consistent field (CASSCF) calculations separately
for each set of singlet and triplet spin symmetries. Within each spin symmetry, averaged natural orbitals were
computed using the CASSCF (6,8) wavefunctions. The final multireference configuration interaction wavefunction
(MRCI) was generated as all single and double excitations from the reference set formed by the all CASSCF
configurations. The core orbitals were kept frozen in all calculations. The atomic basis functions used is the ccpV5Z type developed by Dunning and collaborators. The MRCI wavefunction was constructed by the internally
contracted approach implemented in the MOLPRO suite of programs. This study provides a characterization of a
manifold of potential energy curves, excitation and dissociation energies
72
HOMO and LUMO orbitals for the ground state of the CaSi2 molecule.
Robson A. Simões, Vladir W. Ribas
Departamento de Fı́sica, Instituto Tecnológico de Aeronáutica - ITA, Departamento de Ciência e Tecnologia Aeroespacial,
São José dos Campos, SP, CEP 12228-900, Brazil.
In this work is presented, for the first time, an accurate identification of the HOMO and LUMO orbitals of the
ground state for the CaSi2 molecule. HOMO and LUMO are sometimes referred to as frontier orbitals [1]. We also
are mainly concerned with an accurate spectroscopic characterization of the lowest-lying states of CaSi molecule.
These states correlate with the four lowest dissociation channels. The electronic states of studied triplet symmetry
of the CaSi molecule are those that if correlate with the first and the third channels of dissociation, or either,
Ca (1 Sg) + Si (3 P g) and Ca (3 P u) + Si (3 P g). Results for species like MgSi, BeSi [2] and CaC [3-6] have been
previously reported. The electronic calculations basically involved two steps. The first step consisted of stateaveraged complete active space self-consistent field (CASSCF) calculations separately for each set of singlet and
triplet spin symmetries. Within each spin symmetry, averaged natural orbitals were computed using the CASSCF
(6,8) wavefunctions. The final multireference configuration interaction wavefunction (MRCI) was generated as all
single and double excitations from the reference set formed by the all CASSCF configurations. The core orbitals
were kept frozen in all calculations. The atomic basis functions used is the cc-pV5Z type developed by Dunning
and collaborators. The MRCI wavefunction was constructed by the internally contracted approach implemented
in the MOLPRO suite of programs.
REFERENCES
[1] http://goldbook.iupac.org/F02533.html.
[2] A. I. Boldyrev, J. Simons, J. Phys.Chem. 97 (1993) 1526.
[3] M. Pelegrini, O. Roberto-Neto, F.R. Ornellas, F.B.C. Machado, Chem. Phys. Lett. 383 (2004) 143.
[3] D.T. Halfen, A.J. Apponi, L.M. Ziurys, Astrophys. J. Lett. 577 (2002) L67.
[5] H.H. Takada, M. Pelegrini, O. Roberto-Neto, F.B.C. Machado, Chem. Phys. Lett. 363 (2002) 283.
[6] I.S.K. Kerkines et al., J. Chem. Phys. 117 (2002) 9733.
73
Size-dependent Spin Polarization in P- and B-doped Si Nanocrystals
Maurisan A. Lino, Jeanlex S. de Sousa, G. A. Farias
Dilute magnetic semiconductors (DMS) exhibit great potential for spintronic applications. P-doped Si nanocrystals
(NCs) were experimentally investigasted and shown a strong increase of conductivity due to the doping of individual NCs. P donors contribute to the dark conductivity via spin-dependent hopping, and act as spin-dependent
recombination centers in the photoconductivity measurements [1]. It is already known that it is possible to form
stable magnetism by doping semiconductors with non-magnetic elements. For example, Kwak et al. have shown
C-doped ZnO nanostrutures exhibit size-dependent magnetism. However, the origin of this magnetism it is not
fully understood yet. In this work, we study nearly spherical Si NCs (pure and doped with a single impurity
located at the NC center) with sizes ranging between 1-3 nm with Td symmetry using Density Functional Theory
as implemented in the SIESTA software package [3]. Our results show that both B- and P-doped Si nanocrystals
(NCs) exhibit a size-dependent spin polarization which is reduced as the NC size increases. The magnetic moment
of P-doped NCs is nearly constant for NCs up to 2 nm. For larger sizes the magnetic moment slowly reduces to zero.
For B-doped NCs, the magnetic moment becomes negligible for diameters larger than 2 nm, while P-doped ones
still exhibit non-negligible magnetic moments. The simulation of bulk Si supercells with both impurities resulted
in zero magnetic moment. This allows us to conclude that the appearance of this magnetic moment is exclusively
due to subtle a interplay between the impurity potential with the NC boundaries. We will also discuss the effect
of the impurity localization and higher impurity densities.
[1] A. R. Stegner, R. N. Pereira, K. Klein, R. Dietmueller, M. S. Brandt, M. Stutzmann, Phys. Rev. Lett. 100,
026803 (2008). [2] H. Kwak, J. R. Chelikowsky, Appl. Phys. Lett. 95, 263108 (2009), and references therein. [3]
J. M. Soler, E. Artacho, J. D. Gale, A. Garcı́a, J. Junquera, P. Ordejón, D. Sánchez-Portal, J. Phys.: Condens.
Matter 14, 2745 (2002).
74
First-principles calculation of mechanical and elastic properties of gas hydrates
Paula M. G. L. Ferreira, Caetano R. Miranda
Universidade Federal do ABC
In recent years, natural gas hydrates have drawn significant attention not only as a new natural energy resource
but also as a new economical medium for natural gas storage and transportation. These clathrate hydrates are
cage structured water molecules with guest molecules trapped on it. Unfortunately, an efficient way to recover the
natural gas is difficult because of the hydrates in ocean sediments are dispersed. The main tool to detect hydrate
deposits in the ocean is seismic profiling, which requires a priori the knowledge of hydrates elastic and mechanical
properties. Since the amount and types of guest molecules can vary, it is imperative to know the effects of guest
molecules occupancy on the hydrate mechanical properties, which can be very difficult to measure experimentally.
In this work, we use the first principles calculations within the Density Functional Theory (DFT) to determine
the structural and mechanical properties of cubic sI hydrates with methane and carbon dioxide guest molecules.
Different exchange-correlation functionals have been used BLYP and revPBE generalized gradient approximation
(GGA), that excludes van der Waals forces, and the vdW-DF. For each functional, the lattice parameter, bulk
modulus and elastic constants have been determined to understand the effect of van der Waals interactions on
the host-guest complexes. The calculated bulk modulus with van der Waals corrections was found to be closer to
the experimental data. From the obtained elastic constants, the Young modulus, Poisson ratio and bulk sound
velocities have been determined with respect to type and occupancy of the guest molecules. The calculated values
were compared with speed measurements available and the geophysical consequences explored.
75
Edge states and half-metallicity in TiO2 nanoribbons
André A. Lino
UFPI - PI - Brasil
Hélio Chacham, Mário S. C. Mazzoni
UFMG - MG - Brasil
We apply fisrt-principles calculations to investigate the existence and properties of edge states in TiO2 nanoribbons.
We show that edge states may be found either in the gap region or defining the bottom of the conduction band.
In both cases, the addition of electrons to the ribbons, which is facilitated by the large work function of TiO2
materials, may drive the systems to a half-metallic state, with conduction taking place along the edges and with
only one spin component. We also show that an U-negativity phenomenology may show up in some configurations,
resulting in the stabilization of the charged edges. [1]
Our methodology is based on first-principles electronic structure calculations within the pseudopotential Density
Functional Theory (DFT) [2] formalim. The generalized gradient approximation (GGA) [3] is used as a parametrization for the exchange-correlation functional. We employed the SIESTA implementation [4,5], which makes use
of norm-conserving pseudopotentials [6,7] and a basis set composed of pseudo atomic orbitals of finite range [8].
The geometries are relaxed until the maximum force component is less than 0.1 eV/ Å.
[1] Lino, A. A, Chacham, H., Mazzoni, M, S. C. J. Phys. Chem. C 2011, 115, 18047.
[2] Kohn, W.; Sham, L. J. Phys. Rev. 1965, 140, A1133.
[3] Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865.
[4] Ordejón, P.; Artacho, E.; Soler, J. M. Phys. Rev. B 1996, 53, R10441.
[5] Soler, J. M.; Artacho, E.; Gale, J. G.; Garcia, A.; Junquera, J.; Ordejón, P.; Sánchez-Portal, D. J. Phys.:
Condens. Matt. 2002, 14, 2745.
[6] Troullier, N.; Martins, J. L. Phys. Rev. B 1991, 43, 1993.
[7] Kleinman, L.; Bylander, D. M. Phys. Rev. Lett. 1982, 48, 1425.
[8] We employed a double-ζ basis set, and the range of each orbital was determined by an orbital energy
confinement of 0.01 Ry. Test calculations in which polarization functions were included were not found to introduce
any significant change in our results.
76
A new allotrope of carbon: nanobicones
Mirleide Dantas Lopes, Sérgio André Fontes Azevedo
The amazing properties that carbon has to associate with other carbon atoms in different ways, giving rise to
several allotropes, including carbon nanocones. One hypothetical way to create these nanocones is cut a 60o sector
of graphene, and then glue the cut ends. This procedure will result in a cone with a pentagon at the apex. Observing
that the nanocone referred has non-zero spin polarization and this spin charge is related to the atoms in the region
close to the pentagon is at the apex of the cone, we propose the existence of a new structure made exclusively
with carbon atoms, named carbon nanobicones. The nanobicones are basically nanocones connected by vertex.
When making this direct connection leaves two pentagons at the interface between the nanocones. However, we
investigated, using first-principles calculations based on the density functional theory (DFT), two types of bicones,
one has two pentagons at the interface between the cones and the other has just one. After the connection between
the nanocones the spin polarization of nanobicones goes to zero in both cases. The nanocone has electric dipole
moment it is also canceled after the bicones are created. These characters contribute to provide more stability to
bicones, since we observed that they have approximately the same stability of the cones. The type of connection
made between the cones also contributes to the stability of the bicones. We also observed the effect of impurities
and the applied electric field on the bicones and we found that they cause significant reductions in energy gap.
Thus we conclude that nanobicones likely to be encountered in the nature and they have properties that allow
them to be used in electronic devices.
77
Theoretical study of electronic properties of graphene nano-flakes with H, OH and H2O
functionalization.
Ana Maria Valencia Garcia, Marilia Junqueira Caldas
Instituto de Fisica,Universidade de Sao Paulo
Graphene Nano-Flakes (GNFs), the zero-dimensional (0-D) form of Graphene, present interesting properties, wich
differ from of 2-D Graphene. It was stablished that the stability of GNFs, depends on many factors, size, shape,
charge, temperature and the interaction with the environment [1-4].
We present a systematic theoretical study of the structural and electronic properties of edge functionalization
and impurities, such as hydrogen atom, hydroxyl group and water molecules, absorbed on GNFs. We work within
Density Functional Theory employing a modification of the PBE functional [5], with Tkatchenko-Scheffler (van der
Waals) corrections as implemented in the all-electron package FHI-aims [6]. This code employs numeric atomic
orbitals obtained from ab initio all-electron calculations for isolated atoms, and allows for calculation of both finite
and infinite periodic models.
Here we focus on the description of the electronic properties of GNFs hexagonal strutures wich have a unique
arm-chair edge. As mentioned above, hydrogen, hydroxyl group and water molecules are considered, as well
as, for a periodic infinite system, graphene. To do that, we used a recently proposed strategy [7] to choose an
optimal fraction of exact exchange for the PBE hybrid functional, namely OPBEh [8], that predicts good ionization
potentials and gaps for organic C-H based compounds.
References
[1] Barnard A.S., J.Chem.Phys. 128, 094707 (2008).
[2] Barnard A.S., Carbon. 48, 981 (2010).
[3] Barnard A.S., Nanotechnol. Lett. 3. 59 (2011).
[4] Cocchi C., Ruini A. Prezzi D., Caldas M.J., Molinari E. J.Phys.Chem. C, 115,2969-2973 (2011).
[5] Perdew, J.P. , M. , Phys. Rev. Lett. 77, 3865 (1996).
[6] Blum, V., Gehrke R., Hanke F., Havu P., Havu V., Ren X., Reuter K. and Scheffler M., Comput. Phys.
Comm. 180, 2175 (2009).
[7] Atalla V., Yoo M., Caruso F., Rinke P., Scheffler P., Phys. Rev. B 88, 165122 (2003).
[8] Pinheiro Jr, J.M.F, Caldas, M.J., Rinke, P., Blum, V., to be published.
78
Computational Study of Thermal Conductivity of Si Nanowires
Guilherme Lorenset, Leandro Barros da Silva
As a comparison with other materials and structures, the silicon bulk presents a low thermoelectric efficiency due
to its high thermal conductivity at room temperature. However, the Si nanowire has been studied as a substitute
to Si bulk in electronic devices and thermoelectric applications due to its low thermal conductivity. In this work,
we predict the Si nanowire thermal conductivity κ using the Müller-Plathe method in classical molecular dynamics
simulations. Firstly, we calculated κ for crystalline Si at 500 K, to study the methodology and have a value to
compare the results from Si nanowire. To compute this result, we used the extrapolation linear method found in
the literature. The result for this simulation is about 121.557 W/mK, value this in concordance with the found
in the literature where the experimental results to the value is about 120 W/mK. The study of the Si nanowire
used samples with cross-section area from 4×4 to 6×6 unit cells and length from 10 to 200 uc. Values found to the
4×4 nanowire κ vary from 1.640±0.188 to 3.419±0.053 W/mK, showing that κ varies linearly with the increase
of the length in concordance with the literature found. Second the literature, from the results to κ our system
presents anomalous heat diffusion, violating the Fouriers law. By the increase the cross-section area, is founded
that κ increase too, showing a linear relation between them. The relationship between κ and the temperature of
the system is studied, calculated the nanowire κ to 300, 500 and 1000 K. An inversely proportional relation between
κ and the temperature is founded, alike to the macroscopic scale. Due the different synthetize methods founded
in the literature, we study different geometry shapes of the nanowire cross-section area. The thermal conductivity
from cylindrical and rhombohedral nanowires is calculated to compare with κ from square nanowire. We found a
decrease of about 20% in κ from the cylindrical and rhombohedral nanowires compared to square nanowire. Ours
results show that Si nanowire presents one of the necessary properties to thermoelectric applications, a little thermal
conductance. From this, we hope to accomplish studies about the thermal conductivity in other nanostructures
and materials using our result with the Si nanowire like as a comparison. We expected to calculate and to study
the electric conductivity of these samples using the density functional theory.
79
Electronic transport in three-terminal triangular carbon nanopatches
Ana Luiza Mariano Torres Costa, Vincent Meunier, Eduardo Costa Girão
Universidade Federal do Piauı́, Rensselaer Polytechnic Institute
After the isolation and measurement of individual graphene sheets, in 2004, graphene and related nanostructures
have been the focus of an increasing number of theoretical and experimental studies [1]. As the miniaturization limit
of the electronics based on silicon approaches its limits, alternatives in solid state physics should be investigated
in order to find new materials for this purpose. In this context, graphene and related structures are regarded as
potential candidates to replace silicon technology. Ideal graphene has a zero energy gap, which deserves attention
since the presence of an electronic band gap is fundamental for some applications in nanoelectronics. To this end
we can modify graphenes structure by chemical and/or physical methods in order to create such an opening of
the energy bands around the Fermi level. A widely studied way to make this possible is through the quantum
confinement along one direction in the atomic plane, creating structures called graphene nanoribbons. These
ribbons present electronic properties strongly dependent on their width and edge structure [2]. In this work we
use a combination of Landauer formalism and Greens functions for the calculation of the quantum conductance
in graphitic junctions composed of three terminals made up of GNRs with armchair edges. The Hamiltonian
matrix needed for these calculations is written in a tight-binding approach where interactions are considered up to
third-neighbors away [3]. Here we show how the details of the junction atomic structure influence the transport
properties, as well as we show non-trivial patterns for the electronic current along the structure [4]. We expect
that these results can be part of a larger library of structures which can enable the development of a new class of
nanodevices based on carbon nanostructures.
[1] R. Van Noorden, Nature 469, 14 (2011). [2] Y. W. Son, M. L. Cohen and S. G. Louie, Phys. Rev. Lett.
97, 216803 (2006). [3] D. Gunlycke and C. T. White, Phys. Rev. B 77, 115116 (2008) . [4] A. L. T. Costa et al.,
Nanotechnology 25, 045706 (2014).
80
Doped Boron Nitride Nanoribbons Under Effects of an External Magnetic Field
Duarte José Pereira de Sousa, João Milton Pereira Jr
The research in graphene based structures has stimulated great interest in the investigation of various 2-dimensional
nanomaterials. Among these materials, the 2D hexagonal Boron nitride (h-BN) nanostructures has gained considerable attention. This is because they are the isoelectric analogs to graphene structures and share very similar
structural characteristics and many physical properties except for the large band gap. This makes the h-BN the
perfect candidate to develop technological devices in sets with graphene. The possibility of application of external
fields as well as the doping of nanomaterials has proven a powerful tool for controlling the electronic properties
of these nanostructures. In this work, a theoretical investigation of the electronic properties of doped hexagonal
Boron nitride nanoribbons under the effects of an external magnetic field was performed. The ribbons are made of
lines of Boron and Nitrogen atoms in an armchair or zigzag configurations and the impurities are included in the
ribbon substitutionally. The Peierls approximation is used to incorporate the magnetic field within a tight-binding
picture. It was showed that the aplication of the external field along with the addition of one or two lines of Carbon
atoms as impurities can change drastically the energy spectrum deppending on their localization and the spacing
between them, suggesting a possible mechanism for controlling the gap of such nanomaterials.
81
Interfaces presentes no crescimento de GaN: um estudo ab initio
Mauro Bogéa, Eduardo Moraes, Silvete Guerini
UFMA
Existe um grande interesse comercial e cientı́fico em nitretos semicondutores, pois o grupo de nitretos III-V (AlN,
GaN e InN) estão sendo amplamente aplicados em optoeletrônica e na tecnologia de dispositivos eletrônicos. Dentre
estes o nitreto de gálio (GaN) é provavelmente o material mais interessante, pois pode ser utilizado para na forma de
diodos emissores de luz (LEDs) e transistores de potência elevada, capazes de operar a temperaturas extremamente
altas. Nanomateriais baseados em nitreto de gálio (GaN) tem atraı́do grande atenção por causa do seu grande
potencial para aplicação em spintrônica. Dentre os materiais estudados os nanofios de GaN são os mais promissores
para aplicação em nanotecnologia, por causa de seu largo gap e confinamento estrutural tem grande potencial para
aplicação em emissores de luz ultravioleta, detectores, lasers e dispositivos spintrônicos [1].
Normalmente filmes finos formados por GaN são sintetizados por heteroepitaxia em substratos de safira (Al2 O3 ),
apesar do surgimento de defeitos causados pela diferença entre seus parâmetros de rede. Esses defeitos controlam
subsequentemente toda a dinâmica de sı́ntese dos filmes crescidos por essa técnica e por tanto tem um efeito
significativo nas propriedades óticas e elétricas finais das amostras de GaN crescidas nesse substrato, sendo esse um
comportamento natural de todas as estruturas crescidas por essa técnica. Desse modo, é extremamente importante
caracterizar a região de interface do maior número de modos possı́vel[2].
Neste trabalho apresentamos o estudo das propriedades estruturais de interfaces Al2 O3 /GaN, sendo que a Al2 O3
serve como substrato no processo de crescimento do nitreto de gálio (GaN). Este estudo tem como objetivo melhor
compreender os processo de crescimento do GaN. Os resultados foram realizados através de cálculos de primeiros
princı́pios, usando a teoria do funcional da densidade com a aproximação do gradiente generalizado para o funcional
de troca e correlação. Os cálculos foram realizados utilizando o programa computacional VASP que emprega uma
base de ondas planas. Na caracterização da interface Al2 O3 /GaN verificamos que as propriedades estruturais são
fortemente dependente do straim ao qual o GaN é submetido.
[1] A. Hongkuan Yuan, Hong Chen, Applied Surface Science 256, 6040 (2010). [2] M. Junaid, D. Lundin, et al,
Journal of Applied Physics 110, 123519 (2011).
82
Theoretical investigation of bilayer graphene/Cu(111) interface
Everson S. Souza, Wanderlã L. Scopel, Jair C. C. Freitas
Departamento de Fı́sica, Universidade Federal do Espı́rito Santo, Vitória 299075-910, ES, Brazil
Bernal-stacked bilayer graphene is a promising choice for applications in the nanoscale electronic devices due to the
different ways to control its electronic structure and adjust the bandgap. However, the synthesis of the high-quality
graphene on a large scale is the foundation of its applications. In this sense, the one most popular approach to
prepare single layer, bilayer and few-layers graphene is to grow them on transition metal substrate by chemical
vapor deposition(CVD). The synthesis of bilayer graphene on copper substrate has been successfully performed
[1,2], but the interfacial properties of the bilayer graphene on Cu substrate must be well clarified. Then, we have
examined the energetic stability, electronic and structural properties of bilayer graphene adsorbed on Cu(111)
surface [BLG/Cu(111)] , using density functional theory. In this studies we have considered three different possible
configurations for formation of the interface. Our results have been indicated that the adsorption of bilayer graphene
on Cu(111) surface is guided by a weak physisorption and bottom layer is more attached to Cu(111) surface. We
have found that the most stable configuration has adsorption energy per area of the 39.2 meV/Å2 . This result
is 3.9 meV/Å2 lower than the most stable configuration of single layer graphene on Cu(111) surface, in good
agreement with recently experimental results [3]. Additionally, the formation of BLG/Cu(111) interface gives rise
to the charge density fluctuations and bilayer is n-type doped, such as observed in experimental studies for single
layer graphene on Cu(111) surface [4]. Particularly, we have found (based on Bader charge analysis) that total
doping level of bilayer graphene is 0.0058 e/Å2 (0.0164 e/C) and each layer has a different doping level, namely,
doping level of contacted and uncontacted graphene layer is 0.0048 e/Å2 (0.0136 e/C) and 0.0010 e/Å2 (0.0028
e/C), respectively.
References
[1] K. Yan, H. Peng, Y. Zhou, H. Li and Z. Liu, Nano Lett. 11, 1106 (2011).
[2] L. Liu et al., ACS Nano 6, 8241 (2012).
[3] T. Yoon et al., Nano Lett. 12, 1448 (2012).
[4] A. L. Walter et al., Phys. Rev. B 84, 195443 (2011).
83
Structural and electronic simulation of luminescent lanthanidic metal complexes.
Mateus José Fernandes Martins, Lippy Faria Marques, Flávia Cavalieri Machado, Alexandre Amaral Leitão, Welber
Gianini Quirino
Universidade Federal de Juiz de Fora
The electronics industry is certainly one of the most important segments of the global trade, responsible for moving
billions of dollars annually around the world. All these devices have, as their main base, integrated circuits - better
known as microchips. These components are manufactured mainly with inorganic semiconductor materials, where
the most prominent chemical element is silicon.
However, a new line has established itself in recent years, is organic electronics. What differs this branch of
technology is that traditional inorganic materials have been replaced by organic compounds in the manufacture of
circuits. The main advantage of replacing circuits for organic silicon circuits is the ability to create microchips,
or even microprocessors, highly flexible, since this is a common feature of organic compounds, such as plastic, for
example.
Another important advantage of the development of organic electronics has been the ability to create devices
able to emit light, which are used today for the manufacture of displays. However, many of these organic electroluminescent compounds possess broad emission bands, hindering its application in the manufacture of displays
mentioned. This problem can be circumvented by the use of compounds containing trivalent rare-earth ions.
Given the above, a theoretical study can provide some important information that can be useful in the synthesis
of new organic electronic devices doped with rare-earth metals. This study consists in determining the electronic
structure of new luminescent compounds, in proposing possible reactions leading to their degradation and the
simulation of its thermodynamic potentials obtained, for example, the glass transition temperature.
84
Caracterização topológica do germaneno funcionalizado: Uma investigação de primeiros princı́pios.
Leonardo Batoni Abdalla, Jose Eduardo Padilha de Sousa, Adalberto Fazzio
USP - SP - Brasil
Neste trabalho aborda-se o que é um isolante topológico ou isolante Z2 , e mostra-se quais suas caracterı́sticas
fundamentais e como discriminar um isolante topológico de um trivial via cálculo de invariantes topológicos. Para
tanto ferramentas de topologia de bandas serão abordadas tais com simetria de reversão temporal, fase de Berry e
inversão de bandas via spin órbita. Baseado em cálculos de primeiros princı́pios fizemos uma análise sistemática do
sistema Germaneno funcionalizado com halogêneos. Em todos os casos de funcionalização houve um deslocamento
do cone de Dirac do ponto K para o ponto Γ o que aumenta sua robustez para um defeito que quebre a simetria entre
as sub redes A e B do Germaneno. Além disso as ligações σ da funcionalização promovem uma interação spin órbita
muito mais intensa do que aquele vinda das ligações π do caso pristino. Feito um mapeamento energético, notou-se
uma preferência para a funcionalização com Flúor, porém este sistema em sua forma relaxada não apresenta um
gap topologicamente não trivial. Para o caso funcionalizado com Cloro além de ser o segundo mais estável, o
gap torna-se topológico. É feita uma análise de estrutura de bandas de todos os casos, e calcula-se invariantes
topológicos associados a cada um deles.
85
Caracterização da argila branca de Boa Vista - PB visando a remoção por adsorção de corantes em
solução aquosa
Giovanne de Sousa Monteiro
IF SERTÃO PE / UNIVERSIDADE FEDERAL DE CAMPINA GRANDE
Erivaldo Genuino Lima, Antonielly dos Santos Barbosa, Meiry Gláucia Freire Rodrigues
UNIVERSIDADE FEDERAL DE CAMPINA GRANDE
A argila é um material natural, terroso, de granulação fina e que geralmente adquire, quando umedecido com água,
certa plasticidade. Quimicamente as argilas são formadas essencialmente por silicatos hidratados de alumı́nio,
ferro e magnésio. Na última década, o uso de argilas para adsorção de corantes tem sido objeto de estudo em
uma grande quantidade de trabalhos devido às suas várias vantagens econômicas. Os corantes quando presentes
nos corpos hı́dricos interferem negativamente na demanda quı́mica de oxigênio - DQO e na fotossı́ntese de algas,
além de alguns possuı́rem propriedades carcinogênicas e serem pouco biodegradáveis. Dessa forma, a remoção da
cor dos efluentes é de fato um dos grandes problemas enfrentados pelas indústrias têxteis, isso porque, a elevada
estabilidade biológica dos corantes dificulta sua degradação pelos sistemas convencionais de tratamento, baseados
normalmente em lodo ativo. Esse trabalho visa estudar a argila branca de Boa Vista - PB, através das técnicas
de Capacidade de Troca Catiônica (CTC), Difração de Raios X (DRX) e Microscopia Eletrônica de Varredura
(MEV), com o objetivo de avaliar sua viabilidade na remoção de corantes. Analisando os resultados, observou-se
que o valor da CTC foi de 49,3 meq/g. Pela análise dos resultados do DRX foi observado que a argila branca pode
ser classificada como bentonita, mostrando em 7,82 o pico referente ao grupo. Isso indica que a argila branca pode
ser utilizada na remoção de corantes.
86
EFEITOS SUB -10NM EM TRANSISTORES DE NANOTUBOS DE CARBONO
A. Kirch, M. P. Lima, A. Fazzio, e A. J.R da Silva
USP
Neste trabalho foram realizadas simulações computacionais para investigar as propriedades eletrônicas de um
nanossistema formado por um nanotubo de carbono acoplado a eletrodos de nanofios de paládio encapsulados.
Foi mostrado no presente trabalho, que a inserção do paládio no nanotubo de carbono é energeticamente
favorável em relação aos sistemas isolados. Os metais encapsulados pelo nanotubo de carbono estão protegidos da
oxidação, sendo essa uma vantagem dessa junção em relação aos sistemas não encapsulados. A conexão do paládio
ao nanotubo de carbono resulta em um contato ôhmico, sendo isso desejável para a construção de transistores
de efeito de campo. Essa configuração do nanossistema pode ser importante na construção de transistores de
efeito de campo de alto desempenho. Os resultados das simulações computacionais realizadas para investigar as
propriedades eletrônicas e de transporte desse nanossistema mostraram que: i) estados metálicos do eletrodo se
estendem pela região central e contribuem para a corrente elétrica do nanossistema; ii) os diferentes estados dos
eletrodos influenciam de forma diferente a transmitância do nanossistema, pois possuem diferentes extensões ao
longo do sistema; iii) há mudanças na polarização da corrente, assim como na relação Ion/Ioff com o comprimento
do gate que podem ser explicadas pela diminuição da influência dos estados dos eletrodos na região central; iv)
comprimentos de gate maiores que 2,8 nm são necessários para aplicações lógicas.
Estes resultados sugerem uma nova abordagem para futuros trabalhos no sentido de identificar os estados que
mais se estendem pela região semicondutora, permitindo identificar metais mais apropriados para a construção de
transistores de nanotubos de carbono.
87
Estudos de primeiros princı́pios de nanofio de InAs submetidos a tensões extremas
Leonardo Fernandes Sampaio, Paulo Cesar Piquini
Universidade Federal de Santa Maria - UFSM
Cláudia Lange
Centro Universitario Franciscano - UNIFRA
A manipulação de materiais em nı́veis atômicos com interesse em encontrar novos materias com um desempenho
satisfatório tem crescido exponencialmente. Nossos estudos são focados em nanofios de InAs de diferentes diâmetros
com a finalidade de explorar suas propriedades mecânicas e eletrônicas em situações onde este tipo de material é
submetido a tensões extremas.
Usamos neste trabalho cálculos de primeiros princı́pios baseados na Teoria do Funcional da Densidade (DFT),
implementados nos códido computacional (VASP), usamos a aproximação da densidade local (LDA), para descrever
o termo de troca e correlação.
Nossos resultados mostrão que para o caso compressivo as deformações na estrutura aparecem com aproximadamente com vinte e cinco por cento em todos os diâmetros. Já para o caso distensivo a deformações nas estruturas
aparecem com cerca de vinte por cento para os nanofio de diâmetro maior e para o de menor diâmetro acontece a
quebra total em aproximadamente dezoito por cento, é possı́vel notar a existência de vários intervalos harmônicos
em três casos, chegando a ser reversı́vel dentro de cada intervalo harmônico, e não de intervalo para intervalo.
Na parte eletrônica é possı́vel notar que para os casos distensivos há uma variação positiva no valor (band gap),
chegando em alguns casos as bandas ficarem retas (flat), já na compressão há um estreitamento no valor do band
gap para todos os diâmetros estudados
88
Magnetism in nickel doped tin dioxide
R. A. Bittencourt, J. S. de Almeida
Instituto de Fı́sica - Universidade Federal da Bahia
In this work the electronic and magnetic properties of tin dioxide doped with nickel atoms were theoretically investigated by using first-principles calculations in the framework of density functional theory (DFT) employing the
projector augmented wave (PAW) method as implemented in the Vienna Ab Initio Simulation Package (VASP)
code. The exchange and correlation effects were treated within the generalized gradient approximation (GGA) and
also by including the Hubbard term (GGA+U) to the hamiltonian, which is useful to improve the description of
the localization of d states in transition metal atoms. In order to simulate the doping, four supercells were built up
with the following nickel concentrations: 25%, 12.5%, 6.25%, and 3.125%. For each nickel concentration, one and
two oxygen vacancies were created and considered simultaneously with the doping. The calculations considered
both the ferromagnetic and antiferromagnetic configurations for each nickel concentration.
The results show that tin dioxide doped with nickel remains non magnetic over the entire concentration range
investigated in this work which is also observed by previous studies. This is seen by the analysis of the electronic
structure which shows equally shaped bands for both spin channels in the density of states (DOS) and also by
the total supercell magnetization which completely vanishes for all nickel concentrations. On the other hand, it is
observed that the magnetic ordering of the system is triggered by the creation of oxygen vacancies in the supercells.
For instance, when only one oxygen vacancy is considered in the supercell, the magnetization shows a finite value by
decreasing nickel concentration and the percolation limit is likely to be around 12.5% of nickel with magnetization
of about 2.0 µB . Similarly, for two oxygen vacancies, the system is magnetic at all concentrations considered here
and its magnetization maximum value (4.0 µB ) appears at 6.25% of nickel.
When the Hubbard term (GGA+U) is considered, there are no changes for the system without oxygen vacancies, that is, tin dioxide remains no magnetic for all nickel concentrations. For one and two oxygen vancancies
the behavior of the system is similar to the GGA case. The maximum of magnetization is about 2.0 µB for one
vacancy at 12.5% of nickel concentration while when considering two vacancies the maximum value of 3.3 µB is
found for 6.25% of nickel.
References:
[1] R. A. Bittencourt and J. S. de Almeida, In Manuscript;
[2] H. Wang and et al. J.Appl.Phys., 107:103923 (2010);
[3] J. P. Perdew, K. Burke, and M. Ernzerhof. Phys. Rev. Lett, 77:3865-3868 (1996);
89
Ab initio investigation of F ex Co1−x nanoclusters on a Pt(111) surface: search for magnetic
materials
I. P. Miranda, R. N. Igarashi, H. M. Petrilli
Universidade de São Paulo, Instituto de Fı́sica - DFMT, São Paulo - SP, Brazil
Magnetic materials using 3d metals are promising candidates for applications in high-storage media, especially due
to their interesting properties at the nanoscale. Certain behaviors which play a key role in the design of magnetic
recording devices, such as enhanced anisotropy energy (MAE) and large magnetic moments, were observed for
atomic wires of Co on a Pt surface [1, 2]. Similarly, experimental and theoretical studies of F ex Co1−x monolayers
deposited on a Pt(111) surface have shown large spin moments and high anisotropies compared to F e − Co bulk
(bcc) [3]. Recent investigations of F ex Co1−x nanochains revealed that Fe and Co magnetic moments (spin and
orbital) change with the position of the atom along the chain [4]. Motivated by these results, the magnetic properties of F ex Co1−x nanoclusters on a Pt(111) surface are being investigated using the real space first principles
RS-LMTO-ASA method [5] within the Density Functional Theory (DFT). Our calculations reveal that both spin
and orbital average magnetic moments in triangular F ex Co1−x clusters are described by linear functions of the
Fe concentration (x). Also, for these trimers we verify spin moments close to 3.4µB /atom for Fe and 2.3µB /atom
for Co, and strong ferromagnetic coupling (Jij > 0) between F e − F e, Co − Co and F e − Co nearest neighbors.
Due to the high values of the magnetic moments, we infer that the MAE of F ex Co1−x nanoclusters adsorbed on
a Pt(111) surface can be very large.
References:
[1] P. Gambardella et al., Nature (London) 416, 301 (2002).
[2] A. Enders et al., J. Phys.: Condens. Matter 22, 433001 (2010).
[3] G. Moulas et al., Phys. Rev. B 78, 214424 (2008).
[4] R. N. Igarashi et al., J. Phys.: Condens. Matter 26, 206003 (2014).
[5] S. Frota-Pessôa, Phys. Rev. B 46, 14570 (1992).
90
An ab initio study of eletric properties of linear (HCN)N and (HNC)N aggregates in gas phase
Tertius Lima da Fonseca, Idney Brandão, Marcos Antônio de Castro
Instituto de Fı́sica, Universidade Federal de Goiás
Roberto Rivelino
Instituto de Fı́sica, Universidade Federal da Bahia
The study of nonlinear optical (NLO) responses of molecular systems is an important field of research that have
attracted attention, among other reasons, because of the possibility of developing photonic tecnologies based on
NLO phenomenons. From the quantum chemical point of view, understanding how the microscopic properties
of molecular aggregates change at large extension is a grand challenge. In particular, the convergence of some
molecular properties with the size of the system is only expected for largely extended configurations of molecules. In this sense, HCN and HNC offer both simple and exciting chemical models that allow a refined study by
employing high-level quantum chemical calculations. Using the second-order Møller-Plesset perturbation theory
(MP2) method with the 6-311++G(2d,2p) basis set, we have determined the dipole moment (µ), static linear polarizability (ᾱ) and first hyperpolarizability (βtot and βHRS ) of the following linear chains : (HCN)N and (HNC)N
(for N =1-10). The asymptotic MP2/6-311++G(2d,2p) values of µ, ᾱ, βtot and βHRS per unit (∆µ, ∆ᾱ, ∆βtot and
∆βHRS ) of the chains of HCN and HNC have been estimated using the finite oligomer approach. The obtained
results shows that the effect of the structural isomerization of linear chains of HCN on the polymeric values of ∆µ,
∆ᾱ, ∆βtot and ∆βHRS is significant, principally for these two latter properties. The contribution per unit for the
first hyperpolarizability of the large HNC chains is around 70% larger than the corresponding HCN chains. Our
results also show that the effects of the intermolecular interactions increase the magnitude of the studied electric
properties of both isomers in comparison with the corresponding monomer results.
91
Drugs interacting with BC2 N nanotube: a first principles study
Luiza Goulart, Claudia Lange, Ivana Zanella, Jussane Rossato
In this work we applied first principles density functional calculations to study the interaction between the BC2 N
nanotube armchair (3,3) [1] and the nimesulide and acetylsalicylic acid. These drugs have anti-inflammatory
activity and are usually used for the treatment of acute and chronic inflammatory conditions, but can cause many
adverse reactions [2]. This reactions could be controlled through interaction between them and nanostructured
materials, such as nanotubes BC2 N . Among the numerous applications that nanostructured materials may exhibit,
we highlight the use of nanostructures as drugs carriers. So, in this work we propose to use BC2 N nanotubes as
carriers in order to minimize the side effects of nimesulide and acetylsalicylic acid in the body, so that they can
act on specific sites of action. In this study, we used first-principles calculations using the SIESTA code [3],
based on Density Functional Theory (DFT) and a norm-conserving pseudopotentials. Our results showed that the
interaction between the molecule of nimesulide and nanotube is low (physical adsorption) with binding energies
ranging from -0.27eV to -0.07eV. The interaction between the molecule of acetylsalicylic acid and the nanotube is
low with binding energies ranging from -0.45eV to -0.10eV , characterizing the interaction as weak. These results
show that it is possible to use the BC2 N nanotubes as drug carrier.
REFERENCES
[1] ROSSATO, J. ; BAIERLE, R. J. ; ORELLANA, W. Stability and electronic properties of vacancies and
antisites in BC2 N nanotubes. Physical Review. B, v. 75, p. 235401-1-235401-7, 2007.
[2] ZANELLA, I.; FAGAN, S. B.; MOTA, R.; FAZZIO, A. Ab initio study of pristine and Si-doped capped
carbon nanotube interacting with nimesulide molecules. Chem. Phys. Lett., v. 439, n. 4-6, p. 348 -353, 2007.
[3] SOLER, J. M.; ARTACHO, E.; GALE, J. D.; GARCÍA, A.; JUNQUERA, J.; ORDEJÓN, P.; SÁNCHEZPORTAL, D. The SIESTA method for ab-initio order-N materials simulation. J. Phys.: Condens. Matter v.14,
n. 11, p. 2745-2779, 2002.
92
Effect of M n Incorporation on the Optical Response of CdSe Quantum Dot
Daniel Cesar, Luiz Antônio Cabral, Victor López, Gilmar Marques
Grupo de Nanoestruturas Semicondutoras, Departamento de Fı́sica, Universidade Federal de São Carlos, São Carlos, SP,
Brazil
Eduardo Menéndez
Facultad de Ciencias, Universidad de Chile, Ñuñoa, Santiago, Chile
In this work we have emulated the effect of M n incorporation on the optical response in CdSe quantum dots (QDs)
embedded in a ZnSe matrix by using density functional theory (DFT) calculations. The purpose of the ZnSe
matrix is to preserve the chemical bonds that surround the quantum dot, instead of neutralizing the quantum dot
border atoms with hydrogen. The M n atom enters as a substitutional impurity replacing a Cd atom in the center of
the quantum dot. We observed that according to the energy positions of the QD and M n components, it is possible
that energy of laser-excited electron-hole pairs are transferred into the M n system. This is indeed confirmed when
the absorption coefficient is calculated from the dielectric tensor components obtained in the simulation. Also, the
absorption coefficient of the CdSe:M n QD increased if compared to the analogous system without M n. Although
the dielectric response of the CdSe QD results isotropic, the incorporation of a M n atom resulted in an enhanced
linearly polarized response. Thus, in case of initial polarized excitation of QDs, the light absorption is boosted by
the polarization of the M n-ions. Probing the ratio of the polarization of the laser and the QD emission for different
excitation energies confirm this assumption. The electronic structure was calculated self-consistently using the
projector augmented wave (PAW) [1] method, as implemented in the Vienna Ab-initio Simulation Package (VASP)
[2]. The exchange-correlation functional of Perdew, Burke, and Ernzerhof (PBE) [3] was used, modified by the
on-site Coulomb interaction (PBE+U) in the approximation of Dudarev et al [4].
References:
[1] P. E. Blchl, Phys. Rev. B 50, 17953 (1994).
[2] G. Kresse, J. Furthmuller, Phys. Rev. B 54,11169 (1996).
[3] J. P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996).
[4] S. L. Dudarev, G. A. Botton, S. Y. Savrasov, C. J. Humphreys, and A. P. Sutton, Phys. Rev. B 57, 1505
(1998).
93
Polaronic Effects on the Collective Excitation in a GaAs Parabolic Quantum Wire
Paulo César Miranda Machado
Escola de Engenharia Elétrica, Mecânica e de Computação, Universidade Federal de Goiás, CP 131, 74001-970, Goiânia,
GO, Brazil
Francisco Aparecido Pinto Osório, Antonio Newton Borges
Núcleo de Pesquisa em Fı́sica, Pontifı́cia Universidade Católica de Goiás, Goiânia-GO, Brazil and Instituto de Fı́sica,
Universidade Federal de Goiás,GO-GO, Brazil
Clóves Gonçalves Rodrigues
Núcleo de Pesquisa em Fı́sica, Pontifı́cia Universidade Católica de Goiás, CP 86, 74605-010, Goiânia, Goiás, Brazil
In this work, the plasmon-longitudinal optical (LO) phonon interaction effects on the intrasubband structure factor,
on the pair correlation function and on the intrasubband plasmon energy associated with the lowest subband in
a GaAs parabolic quantum well wire (QWW) are investigated by varying the subband separation energy and the
electronic density. The calculations are performed using the self-consistent field approximation, which includes
the local-field correction within the Singwi, Tosi, Land and Sjölander (STLS) theory, at zero temperature and
assuming a three-subband model where only the first subband is occupied by electrons. The theoretical results
obtained via STLS theory are compared with the random phase approximation (RPA) approach results, in order
to emphasize the importance of the local field corrections (LFC) for the calculation of the collective excitations in
quasi-one-dimensional systems. We have shown that the shape of the intrasubband static structure factor dispersion
relation changes drastically due to the polaronic effect and present dips for low electronic densities. We have also
shown that these dips of the structure factor dispersion relation are directly related to the resonant split of the
intrasubband collective excitation energy, in two branches, one with energy below and other with energy above the
LO-optical phonon energy. We have compared our STLS results for the pair correlation function with those of the
RPA approach and showed that the differences are significant even for densities where the pair-correlation function
calculated via RPA gives positive values. Reference: P. C. M. Machado, F. A. P. Osório and A. N. Borges, Modern
Physics Letters B, vol. 28, no. 12, p. 1450093 (2014). Acknowledgments: We thank Fundação de Apoio à Pesquisa
(FUNAPE-UFG), Fundação de Apoio à Pesquisa do Estado de Goiás (FAPEG) and Pró-Reitoria de Pesquisa e
Pós-Graduação (PROPE) PUC-Goiás for financial support.
94
Drifting Electron Excitation of Acoustic Phonons: Cerenkov-Like Effect in n-GaN
Clóves Gonçalves Rodrigues
Departamento de Matemática e Fı́sica, Pontifı́cia Universidade Católica de Goiás, CP 86, 74605-010 Goiânia, Goiás,
Brazil
Áurea Rosas Vasconcellos, Roberto Luzzi
Condensed Matter Physics Department, Institute of Physics Gleb Wataghin, University of Campinas-Unicamp, Campinas,
SP, Brazil
Some improved methods have recently been developed for generation of coherent terahertz acoustic vibrations
which allow for efficient new possibilities in ultrasonics, with applications in electronics, photonics and in the study
of nanoscale systems. An important particular case is the possibility of phonon ”laser”action in certain system
used in a device called SASER. Several ways to obtain the excitation of the phonon system are available, among
them we center here the attention on drifting electron excitation. That is, non thermal enhanced populations of
phonons in n-doped semiconductors can be achieved by excitation of the phonon system by the transferring of
energy (via the electron-phonon interaction) from the carriers driven out of equilibrium by the presence of intense
electric fields. In this work is considered the process of generation of acoustic phonons by way of drifting electron
excitation in polar semiconductors. Similarly to what is present in lo phonons, the emergence of a condensation
of the pumped energy in modes around an off-center region of the Brillouin zone is evidenced. The phonons are
emitted within a lobe-like distribution with an axis along the direction of the electric field. A numerical calculation
for the case of GaN is done, which shows that the phenomenon can be largely enhanced at high carrier densities
and in strong piezoelectric materials. Reference: C. G. Rodrigues, A. R. Vasconcellos, R. Luzzi, Drifting electron
excitation of acoustic phonons: Cerenkov-like effect in n-GaN, J. Appl. Phys. vol. 113, no. 11, p. 113701 (2013).
Acknowledgments: The authors would like to acknowledge partial financial support received from the São Paulo
State Research Agency (FAPESP) and Goiás State Research Agency (FAPEG).
95
ZnO:Ce structures obtained by sonochemical synthesis and a study of their optical properties
B. C. Costa, P. N Lisboa-Filho
Universidade Estadual Paulista ”Júlio de Mesquita Filho- Unesp, Bauru
Abstract
The variety of technological applications related to semiconducting oxides-based devices has aroused great
interest of the scientific community, making studies related to these materials expand greatly in recent years.
Among these materials, zinc oxide (ZnO) is a semiconductor that has several properties which make it a potential
material for applications in several areas, from light emitting diodes (LEDs) to photovoltaic devices for solar cells [1].
One factor that can influence properties of this material is doping. Particularly, lanthanide (known as rare earths)
doping of ZnO, may offer unique opportunities for improvement in its photosensitive and photoelectrochemical
properties [2]. Hence, it has performed in this work, the characterization (by XRD, SEM and UV-Vis associated
Kulbelka-Munk method analyses) of ZnO samples obtained by sonochemical method, an assisted by ultrasound
chemical synthesis method. An attempt to doping of the samples with Ce ions, in order to modify its optical
properties and an investigation about this effort and ultrasonic treatment time effect on optical properties of these
samples were also performed. Therefore, two samples (pure ZnO, and 1 % at Ce-doped ZnO) were prepared from
sonochemical method using the commercial powders of zinc and cerium oxides as precursors reagents. Similarly,
two samples (pure ZnO and 1 at % Ce-doped ZnO) were also prepared from zinc and cerium nitrates as precursors
reagents. The obtained results suggest that sonochemical synthesis method, with use of a low power ultrasound
irradiation, was not effective for rare earth elements incorporation in the ZnO matrix, since a surface and no
significant incorporation was observed for samples synthesized in this work. Furthermore, as a consequence of no
doping atoms incorporation, any changes were observed in band gap values for samples with Ce addition in the
Kubelka-Munk plots.
References:
[1] Janotti, A., Van de Walle, C. G. Reports on Progress in Physics, 72, (2009).
[2] Panda, N. R., Achayra, B. S., Singh, T. B., Gartia, R. K. Journal of Luminescence, 136, 369-377, (2013).
96
Dynamics of few interacting particles: tunneling and correlation effects
Mariana Mieko Odashima
The dynamics of interacting particles is a fascinating problem. New achievements in ultrafast dynamics, atomic
gases, low-dimensional physics, and quantum information flourish every year, revealing new effects in the nano
and mesoscale. The quantum mechanical description of the electronic dynamics can be approached by correlated
methods such as density-functional theory in its time-dependent version. However, already in the electronic structure context, describing the correlations through semilocal density functional approximations is a very intricate
task. The evolution of the electronic system can show also new correlations or so-called memory effects, but so far
not much is known about how to build functionals with time dependence. The computational cost for obtaining
exact results is also very limiting, most works depart from systems with few degrees of freedom or model Hamiltonians. Here we study the exact dynamics of two repulsively interacting particles in one dimension with a numerical
time-dependent approach, examining a very fundamental quantum mechanical problem, quantum tunneling. Tunneling is at the heart of many dynamical processes such as quantum decay or particle loss, transport in tunnel
junctions, chemical or nuclear fusion reactions. We would like to shed some light on the dynamics of interacting
particles and how our functionals behave in time.
97
Electronic and magnetic properties of small scandium clusters
N. L. Moreira
Universidade Federal de Goiás
The size dependence of the properties of small clusters as a interplay between atomic-like and solid-like ones has
been a subject of intense study due a large spectrum of application of these materials in condensed matter physics
covering magnetic material design, chemical catalysis and other suitable industrial applications.
Within this class of materials, the transition metals has received a lot of attention of the researchers in despite of
the difficulties imposed by the unfilled d shell that result in a number of isomers too close in energy. The Scandium
(Sc) is a 3d transition metal that has received considerable attention because in the bulk phase it is a paramagnetic
solid, however when atoms is brought up to form few atoms cluster it presents an enhanced magnetic moment.
Recent Stern-Gerlach molecular-beam deflections studies reports magnetic moment about 6, 0 ± 0.2µB for Sc13
cluster. However the magnetic properties are related intrinsically with the lowest energy geometrical structure and
correspondent electronic structure. Therefore the scandium clusters may serve as an ideal system to understand
the interplay among size, geometry, electronic structure, and magnetism. The structural and magnetic properties
of small pure scandium clusters was studied by Yuan et all (PRB 74,2006) and Wang (PRB 75, 2007). However,
the lowest energy structure of Sc9 and the multiplicity of Sc6 , Sc8 are not consistent with each other. The only
work beyond those due to Fu-Yang et all (PRB 77, 2008) is in agreement with Yuan to the multiplicity of Sc6 but
not for Sc8 or agreement with Wang for the multiplicity of the Sc8 but not for SC6 and therefore are not conclusive.
In this work we have studied the geometric, magnetic and electronic structures of the Scn clusters with n ≤ 9
by Density Functional Theory (DFT) and Quantum Monte Carlo (QMC) Simulations.
98
Propriedades de transporte eletronico em nanotubos de carbono com poros poligonais
Jeová Calisto dos Santos, Fabrı́cio Morais de Vasconcelos, Acrı́sio Lins de Aguiar, Eduardo Costa Girão
UFPI
The study of carbon nanostructures have shown the potential that these materials have to compose integrated
electronic circuits. In the case of carbon nanotubes, it is known that there is a relationship between their behavior
(metallic or semiconducting) with (n, m) index that characterize them. In this work, we used the tight-binding
model added to a Hubbard Hamiltonian, together with the Landauer and Green’s functions formalisms, to investigate the electronic transport properties in carbon nanotubes containing polygonal pores (defects). We studied a
armchair (12,12) nanotube with a single pore on his wall, with three possibilities for the pore geometry: lozenge,
triangle or hexagon. In these structures, the defect consists in the removel of a specific number of atoms from
the nanotube surface to form the pore. In addition, we considered different spin-polarized configurations for the
pores zigzag edges, resulting in different magnetic states and electronic transport properties for each system. We
observe complex behaviors for the electronic transmission for each (pore geometry)/(pore size)/(magnetic state)
combination. We also show that these defective structures can be considered prototypes to the development of
devices aiming the control of the electronic flux along the system, or, in other words, systems which offer the possibility of adjusting the transport properties of the nanotubes by the choice of details of the defect atomic structure,
magnetic state and electronic spin.
99
ESTUDO AB INITIO DO DMACA E DO PHENOL BLUE EM ÁGUA
Leandro Rezende Franco, Herbert de Castro Georg
Instituto de Fı́sica, Universidade Federal de Goiás, CP 131, 74001-970, Goiânia, GO.
Neste trabalho apresentaremos um estudo da estrutura conformacional e eletrônica de duas moléculas
sensı́veis ao ambiente, o p-dimetilamino-cinnamaldeı́do (DMACA) e o phenol blue (PB) em meio aquoso.
Para esse estudo utilizamos duas metodologias diferentes para levar em conta o meio aquoso. Um modelo
contı́nuo polarizável (PCM) [1] e um modelo discreto baseado no método QM/MM sequencial usando simulações
de Monte Carlo Metropolis [2], no método de campo médio ASEC [3] e no método de Gradiente de Energia Livre
(FEG) [4].
Em ambos os casos, com o modelo PCM obtivemos mudanças pouco significativas na geometria das
moléculas ao passar da molécula isolada para a fase aquosa. Já usando o modelo discreto observamos mudanças
bastante significativas nas duas moléculas ao passar para a fase aquosa. No caso do DMACA as ligações C=C
aumentam seu comprimento enquanto as ligações C-C diminuem, e ficam a meio caminho de igualarem-se. No
caso do PB a mudança é ainda maior e há uma equiparação entre as ligações originalmente apontadas como N-C
e N=C, ficando a ligação N=C ligeiramente maior que a N-C.
Cálculos de energia de excitação foram realizados com TD-DFT, utilizando os funcionais CAM-B3LYP
e BHandHLYP, para comparar a geometria PCM com a geometria ASEC-FEG.
Para o DMACA os cálculos de desvio solvatocrômico não nos permitiram concluir sobre a estrutura da
molécula em solução. No caso do PB, entretanto, os cálculos de desvio solvatocrômico indicam que a geometria
ASEC-FEG representa melhor a estrutura da molécula em solução e que portanto há uma mudança grande na
estrutura das ligações simples e duplas conjugadas e nos anéis aromático e quinoidal da molécula quando em
solução. Isso pode ter consequências importantes nas propriedades não lineares da molécula, o que está sendo
investigado no nosso grupo.
Referências
[1] Miertus, S.; Scrocco, E.; Tomasi, J. Chem. Phys. 55 (1981) 117-129.
[2] Coutinho, K.; Rivelino, R.; Georg, H.C.; Canuto, S. In: Canuto, S. (Org.), Solvation Effects in Molecules and
Biomolecules. Challenges and Advances in Computational Chemistry and Physics. Springer, 2008, v. 6, 159-189.
[3] Coutinho, K.; Georg, H.C.; Fonseca, T.L.; Ludwig, V.; Canuto, S. Chem. Phys. Lett. 437 (2007) 148-152.
[4] Okuyama-Yoshida, N.; Nagaoka, M.; Yamabe, T. Int. J. Quantum Chem. 70 (1998) 95-103.
Apoio: Capes, CNPq, FAPEG
100
Optical Absorption of Silane Derivative Molecular Systems
Maria Isabel Oliveira
Instituto Federal da Bahia - IFBA
Roberto Rivelino, F. de B. Mota
Gueogui Gueorguiev
Linköping University
We have performed first-principle calculations to study the optical properties of compounds containing silicon
carbon covalent interactions. In this work, we investigate the geometry, size and composition effects on the
electronic and optical properties of oligosilanes and persilastaffanes, which can be used as nanounits to build up
semiconductor nanostructures. Our main goal is to investigate the many-body effects on the optical absorption
of these compounds and discuss the viability of applications in optical sensor nanodevices. In our study, initially,
the geometry optimization and electronic structure calculations of all systems considered here were performed
at the level of the density functional theory (DFT) within the full-potential projector augmented wave method
(PAW). Then, the quasiparticle interaction corrections were included via Green’s function, specifically by means
of GW approximation (where G = one particle Green’s function and W = ε−1 v, i.e., the screened Coulomb
interaction). Thereby, the DFT Kohn-Sham energy levels are corrected from the exchange and correlation selfenergy, Σ, iteratively calculated within the GW approximation, with Σ = iGW . In a third stage (including the
electron-hole interactions), the optical spectra of some of these compounds were also calculated by solving the BetheSalpeter equation. The quasiparticle corrections show that the electronic gap of these materials are drastically
enlarged when compared to the electronic gap obtained via DFT. Our results suggest that, even considering a
scale of nanostructures, these compounds (oligosilanes or persilastaffanes) should give rise to stable and robust
semiconductor materials with potential applications in optical devices.
101
Effects of van der Waals corrections on electronic structure and interaction in different mixtures of
argon and xenon under supercritical conditions
V. O. Damião, F. de B. Mota, R. Rivelino
Recently, great advances have been made in modeling solubilities and phase behavior of supercritical fluid mixtures.
In this work, thermodynamic, structural, and electronic properties of argon, xenon and their binary mixtures under
supercritical conditions were studied via atomistic computational simulations. The behavior of these systems
was investigated for different thermodynamic conditions and concentrations (in the case of binary mixtures).
Furthermore, the variation of the thermodynamic properties with the concentration was thoroughly investigated
under supercritical conditions. Our simulations were carried out within the classical Monte Carlo Metropolis
method with appropriate Lennard-Jones potential models. Statistically uncorrelated configurations resultant from
the classical simulations were employed as input for further quantum-mechanical calculations, which was performed
within density functional theory (DFT). Thus, cohesive energy and electronic structure for the different supercritical
phases of the systems were calculated with the sequential QM/MM method (S-QM/MM). The effect of dispersion
corrections in DFT was evaluated by using the Grimme method (DFT-D, as implemented in the SIESTA code). The
interaction parameters were properly adjusted from the dissociation curves of Ar2 , Xe2 , and ArXe dimers. The SQM/MM calculations were performed considering cubic boxes containing 400 atoms for each system, preserving the
spatial configurations of the supercritical conditions. All the calculations were performed with periodic boundary
conditions. Our results have shown that the inclusion of dispersion effects significantly increases the cohesive
energy, especially for the systems containing xenon, whereas the electronic structure is essentially insensitive.
102
Magnetic field dependence of the energy levels in bilayer graphene nano-flakes
D. R. da Costa, A. Chaves, G. A. Farias
UFC - CE - Brasil
M. Zarenia, F. M. Peeters
University of Antwerp - Antwerpen - Belgium
Very soon after the discovery of graphene [1], theoretical and experimental studies appeared on graphene
quantum dots (GQDs). GQDs can be exceptional systems for spintronics applications due to their long spin
coherence time which is a consequence of the very weak spin-orbit interaction in graphene. Alternatively, bilayer
graphene flakes are another type of QDs which may exhibit very different properties but which have been barely
studied [2, 3]. A system very similar to circular single layer GQDs where confinement was realized by using the
infinite-mass boundary condition was investigated half a century ago by Berry and Mondragon [4] as a theoretical
example for the confinement of neutrino’s. The virtues of such a boundary condition have been already discussed
for monolayer graphene QDs [5, 6]. To our knowledge no equivalent study has been made for QDs in BLG. The
possible reason for this can be traced back to the non availability of appropriate boundary conditions.
Using the four-band continuum model we derive a general expression for the infinite-mass boundary condition in bilayer graphene. Applying this new boundary condition we analytically calculate the confined states and
the corresponding wave functions in a bilayer graphene quantum dot in the absence and presence of a perpendicular
magnetic field. Our results for the energy spectrum show an energy gap between the electron and hole states at
small magnetic fields. Furthermore the electron (e) and hole (h) energy levels corresponding to the K and K ′
e(h)
h(e)
valleys exhibit the EK (m) = −EK ′ (m) symmetry, where m is the angular momentum quantum number.
References
[1] K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, and A.
A. Firsov, Science 306, 666 (2004).
[2] A. D. Güçlü, P. Potasz, and P. Hawrylak. Phys. Rev. B 84, 035425 (2011).
[3] D. P. Zebrowski, E. Wach, and B. Szafran, Phys. Rev. B 88, 165405 (2013).
[4] M. V. Berry and R. J. Mondragon, Proc. R. Soc. London, Ser. A 412, 53 (1987).
[5] S. Schnez, K. Ensslin, M. Sigrist, and T. Ihn, Phys. Rev. B 78, 195427 (2008).
[6] M. Grujić, M. Zarenia, A. Chaves, M. Tadić, G. A. Farias, and F. M. Peeters, Phys. Rev. B 84, 205441
(2011).
103
Comparative study of single layer Ni(111) deposited on graphene and graphene/Ni(111) system
Sabrina S. Carara, Teldo A. S. Pereira, Luis Craco
Universidade Federal de Mato Grosso, Mato Grosso, Brasil
Recent experiments [1,2] have proposed new systems where the substrate employed is graphene. Motivated
thereby, we perform a comparative study between a single layer of Ni(111) deposited on a graphene monolayer with
that composed by a graphene monolayer deposited on a Ni(111) surface [3,4]. We study the electronic, structural and
magnetic properties of a single layer of Ni(111) on top of graphene comparing it with the known graphene/Ni(111)
system by first-principle calculations. Our aim is to show whether the interaction between graphene and the
Ni(111) surface is dependable of the stacking and the number of Ni(111) layers or not. Our aim is to investigate
various physical properties in both systems, including the formation of local magnetic moments, orbital-selective
and Dirac-like bandgaps, interatomic distances, etc. Our methodology is based on density functional theory within
the generalized gradient approximation and norm-conserving pseudopotentials as implemented in Siesta code. The
basis set is a linear combination of pseudoatomic orbitals of finite range. Our results for the energy gaps and total
energies will be obtained with a split-valence double-zeta basis, including polarization functions.
References:
[1]
[2]
[3]
[4]
G. Lupina et al., Appl. Phys. Lett. 103, 183116 (2013).
M. Sicot et al., Appl. Phys. Lett. 96, 093115 (2010).
Yu. S. Dedkov et al., Appl. Phys. Lett. 92, 052506 (2008).
L. V. Dzemiantsova et al., Phys. Rev. B 84, 205431 (2011).
104
Time-evolution of wave-packets in topological insulators
Gerson J. Ferreira
Instituto de Fı́sica, Universidade Federal de Uberlândia
Poliana H. Penteado, J. Carlos Egues
Instituto de Fı́sica de São Carlos, Universidade de São Paulo
Time-reversal topological insulators (TIs) are a fantastic new class of narrow-band semiconductors that have gapless
helical surface (3D TIs) or edge (2D TIs) states embedded within the bulk gap of its host material. This unique
property are present in materials with strong spin-orbit coupling (SOC), and they are classified accordingly to the
Z2 invariant. The gapless helical states rise at the interface between materials with different Z2 . Due to the strong
spin-orbit coupling, the motion of the electrons on these topological insulators is correlated with their spins, yielding
for instance the quantum anomalous Hall effect [1]. Here we investigate the ballistic time-evolution of wave-packets
in topological insulators. Within the Dirac equation, the interference between eigenstates from positive and negative
energy bands leads to the relativistic oscillatory motion of electrons well known as Zitterbewegung. Equivalent
effects are expected in graphene and topological insulators. Here we calculate the ballistic time-evolution of wavepackets in topological insulators under different conditions including electric field, boundaries, and magnetic fields.
In the limit of wide wave-packets a simple approach in terms of the Ehrenfest theorem is satisfactory and show
most of the qualitative aspects of the results. For narrow wave-packets or systems with boundaries we propagate
the full wave-packet. Our results show that even though there are edge states on the system, the edge-bulk coupling
is strong due to the narrow gap and the Zener tunneling due to the electric field, plus the Zitterbewegung show
non-trivial transport.
We acknowledge support from the Pró-Reitoria de Pesquisa (PRP/USP) within the Research Support Center
Initiative (NAP Q-NANO), CNPq and FAPEMIG.
[1] Gerson J. Ferreira, Daniel Loss, Phys. Rev. Lett. 111, 106802 (2013)

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