HORACIO WAGNER LEITE ALVES | UFSJ - Federal University of São João Del-Rei (original) (raw)

Papers by HORACIO WAGNER LEITE ALVES

Research paper thumbnail of Deep levels associated with vacancy and nitrogen in diamond

Neste trabalho estudamos a estrutura eletrônica de defeitos pontuais em diamante , os quais intro... more Neste trabalho estudamos a estrutura eletrônica de defeitos pontuais em diamante , os quais introduzem níveis profundos na faixa proibida deste material. Utilizamos o modelo de aglomerado molecular dentro de dois formalismos: o Método do Espalhamento Múltiplo X (MS- X), que é um método de primeiros princípios e o método \"Complete Neglect of Differential Overlap\" (CNDO/ BW), que é semi-empírico. Foi empregado um tratamento adequado para os orbitais de superfície em cada um dos dois formalismos . Foram estudados dois sistemas: o Nitrogênio substitucional e a vacância simples. Para o Nitrogênio, analisamos as possíveis distorções associadas a este centro, procurando interpretar os resultados experimentais. A vacância simples mostrou-se ser um sistema bastante semelhante à vacância simples em Silício: em ambos os casos observa - se uma distorção Jahn-Teller. O modelo adotado mostrou- se capaz de descrever satisfatoriamente as estruturas eletrônicas dos dois centros estudados...

Research paper thumbnail of Structural and electronic properties of vacancies and impurities in non-passivated silicon nanowires by first-principles calculations

Proceedings of Brazilian Workshop on Semiconductor Physics

In this work, we report our preliminary results for the presence of the vacancy, as well as for t... more In this work, we report our preliminary results for the presence of the vacancy, as well as for the boron and nitrogen impurities in non-passivated [001] silicon nanowires. The results show that defects and dopants tend to segregate to the nanowire surfaces, as observed for passivated [110] ones, but at the (-2) charge state, due to the metallic character of the [001] nanowire. The vacancies are stable at the facets, while the impurities stay preferentially at the interstitial site, making bridges with the lateral surface Si atoms, below to this surface. As a consequence, the surface -states located at the facets are filled and a small bandgap appears in the calculated defect band structures.

Research paper thumbnail of Molecular Signature in the Photoluminescence of α-Glycine, L-Alanine and L-Asparagine Crystals: Detection, ab initio Calculations, and Bio-sensor Applications

AIP Conference Proceedings

We present the photoluminescence spectra of α-glycine, L-alanine, and L-asparagine crystals. They... more We present the photoluminescence spectra of α-glycine, L-alanine, and L-asparagine crystals. They are broad and structured, comprising green to ultraviolet emission in the 1.75–3.60 eV range. Absorption measurements show that the band gap energies of the crystals are of the order of 5.0 eV. Ab initio calculations of their electronic structures allow for the assignment of the observed peaks in the visible region to lattice-related processes of exciton nature associated with polaron levels. The very thin photoluminescence peaks in the ultraviolet region are assigned to intramolecular transitions, being a signature of the weakly interacting amino acid molecules in the crystals.

Research paper thumbnail of Ab initio Results for the Structural and Electronic Properties of Intrinsic Defects in PbTe

In this work, we have performed spin-polarized calculations for the structural and electronic pro... more In this work, we have performed spin-polarized calculations for the structural and electronic properties of vacancies and anti-site defects in the rocksalt PbTe. Our obtained results have shown that both the Pb and Te antisites are the favorable defects in Pb and Te rich conditions, respectively. Moreover, in the perfect stoichiometry condition, the antisites, as well as the Te vacancy, are equally probable to find. Considering the charge injection in the system, all the defects change from the 2+ charge state to the 2one within 14 meV, at around 80 meV from the valence band edge within the bandgap. This feature makes it difficult to experimentally characterize these defects in PbTe.

Research paper thumbnail of Obtaining the magnetic susceptibility of the heme complex from DFT calculations

AIP Advances

Magnetic field interactions with particles, as observed in magnetophoresis, are becoming importan... more Magnetic field interactions with particles, as observed in magnetophoresis, are becoming important tool to understand the nature of the iron role in heme molecular complex, besides other useful applications. Accurate estimations of some macroscopic magnetic properties from quantum mechanical calculations, such as the magnetic susceptibility, can also check the reliability of the heme microscopic models. In this work we report, by using the Stoner criterion, a simple way to obtain the magnetic susceptibility of the heme complex from Density Functional Theory calculations. Some of our calculated structural properties and electronic structure show good agreement with both the available experimental and theoretical data, and the results show that its groundstate is a triplet 3 A state. From the obtained results, we have evaluated the exchange interaction energy, J = 0.98 eV, the associated magnetic energy gain, ∆E M = −0.68 eV, and the magnetic susceptibility, χ 0 = 1.73 × 10 −6 cm 3 /mol for the heme alone (with uncompleted Fe ligands). If we consider the heme complex with the two histidine residues (completing the Fe ligands), we have then obtained χ 0 = 5.27 × 10 −12 cm 3 /g, which is in good agreement with experimental magnetophoresis data.

Research paper thumbnail of Structural and Electronic Properties of Vacancies and Impurities in non- passivated Silicon Nanowires by first-principles calculations

18TH BRAZILIAN WORKSHOP ON SEMICONDUCTOR PHYSICS, 2017

In this work, we report our preliminary results for the presence of the vacancy, as well as for t... more In this work, we report our preliminary results for the presence of the vacancy, as well as for the boron and nitrogen impurities in non-passivated [001] silicon nanowires. The results show that defects and dopants tend to segregate to the nanowire surfaces, as observed for passivated [110] ones, but at the (-2) charge state, due to the metallic character of the [001] nanowire. The vacancies are stable at the facets, while the impurities stay preferentially at the interstitial site, making bridges with the lateral surface Si atoms, below to this surface. As a consequence, the surface -states located at the facets are filled and a small bandgap appears in the calculated defect band structures.

Research paper thumbnail of Theoretical study of Sn and Te adsorption over graphene from ab initio calculations

AIP Advances

In this work, we report on theoretical calculations for the adsorption of both Sn and Te atoms ov... more In this work, we report on theoretical calculations for the adsorption of both Sn and Te atoms over a graphene monolayer. Our obtained results show that Sn is chemisorbed over a graphene CC bond, once the presence of Sn over the substrate changes some of graphene's CC sp 2-like bond character to a more covalently reactive sp 3-like one. On the other hand, Te is physisorbed over a C atom of the graphene sheet, since it is weakly connected to the surface atoms by van der Waals' forces. However, both Sn and Te are extremely mobile over the graphene monolayer because the energy barriers between the adsorption sites are very small. Considering that SiC surfaces passivated with graphene enhance the strength of the C-Sn bonds in the MBE growth procedure, our results, theoretically, confirm the growth of a SnTe layer on graphene.

Research paper thumbnail of Interplay between magnetic, metal/insulator and topological phases in Hg1-xMnxTe alloys: prediction of a ferromagnetic Weyl semimetal at x= 0.25

Journal of Physics: Condensed Matter

Research paper thumbnail of Vibrational properties of cubic Inx Ga1-xN structures

Research paper thumbnail of Structural, electronic, and optical properties of ZrO2 from ab initio calculations

Journal of Applied Physics, 2006

Structural, electronic, and optical properties for the cubic, tetragonal, and monoclinic crystall... more Structural, electronic, and optical properties for the cubic, tetragonal, and monoclinic crystalline phases of ZrO2, as derived from ab initio full-relativistic calculations, are presented. The electronic structure calculations were carried out by means of the all-electron full-potential linear augmented plane wave method, within the framework of the density functional theory and the local density approximation. The calculated carrier effective masses

Research paper thumbnail of Molecular Signature in the Photoluminescence of alpha-Glycine, L-Alanine and L-Asparagine Crystals: Detection, ab initio Calculations, and Biosensor Applications

We present the photoluminescence spectra of alpha-glycine, L-alanine, and L-asparagine crystals. ... more We present the photoluminescence spectra of alpha-glycine, L-alanine, and L-asparagine crystals. They are broad and structured, comprising green to ultraviolet emission in the 1.75-3.60 eV range. Absorption measurements show that the band gap energies of the crystals are of the order of 5.0 eV. Ab initio calculations of their electronic structures allow for the assignment of the observed peaks in

Research paper thumbnail of Structural and Electronic Properties of Vacancies and Impurities in non- passivated Silicon Nanowires by first-principles calculations

18TH BRAZILIAN WORKSHOP ON SEMICONDUCTOR PHYSICS, 2017

In this work, we report our preliminary results for the presence of the vacancy, as well as for t... more In this work, we report our preliminary results for the presence of the vacancy, as well as for the boron and nitrogen impurities in non-passivated [001] silicon nanowires. The results show that defects and dopants tend to segregate to the nanowire surfaces, as observed for passivated [110] ones, but at the (-2) charge state, due to the metallic character of the [001] nanowire. The vacancies are stable at the facets, while the impurities stay preferentially at the interstitial site, making bridges with the lateral surface Si atoms, below to this surface. As a consequence, the surface -states located at the facets are filled and a small bandgap appears in the calculated defect band structures.

Research paper thumbnail of Ab initio Results for the Structural and Electronic Properties of Intrinsic Defects in PbTe

18TH BRAZILIAN WORKSHOP ON SEMICONDUCTOR PHYSICS, 2017

In this work, we have performed spin-polarized calculations for the structural and electronic pro... more In this work, we have performed spin-polarized calculations for the structural and electronic properties of vacancies and anti-site defects in the rocksalt PbTe. Our obtained results have shown that both the Pb and Te antisites are the favorable defects in Pb and Te rich conditions, respectively. Moreover, in the perfect stoichiometry condition, the anti-sites, as well as the Te vacancy, are equally probable to find. Considering the charge injection in the system, all the defects change from the 2+ charge state to the 2-one within 14 meV, at around 80 meV from the valence band edge within the bandgap. This feature makes it difficult to experimentally characterize these defects in PbTe.

Research paper thumbnail of Obtaining the magnetic susceptibility of the heme complex from DFT calculations

Magnetic field interactions with particles, as observed in magnetophoresis, are becoming importan... more Magnetic field interactions with particles, as observed in magnetophoresis, are becoming important tool to understand the nature of the iron role in heme molecular complex, besides other useful applications. Accurate estimations of some macroscopic magnetic properties from quantum mechanical calculations, such as the magnetic susceptibility , can also check the reliability of the heme microscopic models. In this work we report, by using the Stoner criterion, a simple way to obtain the magnetic susceptibility of the heme complex from Density Functional Theory calculations. Some of our calculated structural properties and electronic structure show good agreement with both the available experimental and theoretical data, and the results show that its groundstate is a triplet 3 A state. From the obtained results, we have evaluated the exchange interaction energy, J = 0.98 eV, the associated magnetic energy gain, ∆E M = −0.68 eV, and the magnetic susceptibility, χ 0 = 1.73 × 10 −6 cm 3 /mol for the heme alone (with uncompleted Fe ligands). If we consider the heme complex with the two histidine residues (completing the Fe ligands), we have then obtained χ 0 = 5.27 × 10 −12 cm 3 /g, which is in good agreement with experimental magnetophoresis data. © 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license

Research paper thumbnail of Structural, electronic, vibrational, and dielectric properties of LaBGeO5 from first principles

Journal of Applied Physics, 2014

Research paper thumbnail of Ab initio calculation of the dynamical properties of GaAs and GaN (110) and (100) surfaces

Journal of Physics Conference Series

In this work, we have calculated the vibrational modes and frequencies of the crystalline PPP (in... more In this work, we have calculated the vibrational modes and frequencies of the crystalline PPP (in both the Pbam and Pnnm symmetries) and PPV (in the P2 1 /c symmetry). Our results are in good agreement with the available experimental data. Also, we have calculated the temperature dependence of their specific heats at constant volume, and of their vibrational entropies. Based on our results, at high temperatures, the PPP is more stable in the Pnnm structure than in the Pbam

Research paper thumbnail of Níveis profundos associados a vacância e nitrogênio em diamante

Research paper thumbnail of Interchain Effects on the Vibrational Properties of PPP and PPV

AIP Conference Proceedings

In this work, we have calculated the vibrational modes of the poly-paraphenylene (PPP) in both Pb... more In this work, we have calculated the vibrational modes of the poly-paraphenylene (PPP) in both Pbam and Pnnm structures, and of the poly-paraphenylene-vinylene (PPV) in the P2 1 /c structure. Our results agree well (within 3 % of error) with the available experimental data, whenever these comparison is possible. Based on our calculations, we show that the acoustical longitudinal mode stretches the π-bonds, while the acoustical transversal ones leads only to their torsion.

Research paper thumbnail of Electronic Structure of Point Defects in SiC

Brazilian Journal of Physics

In this work we h a ve calculated the electronic structure of point defects in cubic silicon carb... more In this work we h a ve calculated the electronic structure of point defects in cubic silicon carbide(3C-SiC) using the Molecular Cluster Model within the framework of the ab initio LCAO-MO Unrestricted Hartree-Fock method. The following point defects were studied: vacancies, anti-sites, Si and C interstitials at both tetrahedral and hexagonal sites. Our results show good agreement with both experimental and other theoretical calcula-tions. From the total energy evaluation, without including relaxation and/or local distortion eeects, we found that carbon anti-site and silicon vacancy are the most energetically stable point defects in both C-rich and stoichiometrically 3C-SiC, while for Si-rich material, silicon anti-site and carbon vacancy are the most stable ones.

Research paper thumbnail of Thermoelectric properties of IV–VI-based heterostructures and superlattices

Journal of Solid State Chemistry

Doping in a manner that introduces anisotropy in order to reduce thermal conductivity is a signif... more Doping in a manner that introduces anisotropy in order to reduce thermal conductivity is a significant focus in thermoelectric research today. By solving the semiclassical Boltzmann transport equations in the constant scattering time (τ) approximation, in conjunction with ab initio electronic structure calculations, within Density Functional Theory, we compare the Seebeck coefficient (S) and figure of merit (ZT) of bulk PbTe to PbTe/SnTe/PbTe heterostructures and PbTe doping superlattices (SLs) with periodically doped planes. Bismuth and Thallium were used as the n- and p-type impurities, respectively. The effects of carrier concentration are considered via chemical potential variation in a rigid band approximation. The impurity bands near the Fermi level in the electronic structure of PbTe SLs are of Tl s- and Bi p-character, and this feature is independent of the doping concentration or the distance between impurity planes. We observe the impurity bands to have a metallic nature i...

Research paper thumbnail of Deep levels associated with vacancy and nitrogen in diamond

Neste trabalho estudamos a estrutura eletrônica de defeitos pontuais em diamante , os quais intro... more Neste trabalho estudamos a estrutura eletrônica de defeitos pontuais em diamante , os quais introduzem níveis profundos na faixa proibida deste material. Utilizamos o modelo de aglomerado molecular dentro de dois formalismos: o Método do Espalhamento Múltiplo X (MS- X), que é um método de primeiros princípios e o método \"Complete Neglect of Differential Overlap\" (CNDO/ BW), que é semi-empírico. Foi empregado um tratamento adequado para os orbitais de superfície em cada um dos dois formalismos . Foram estudados dois sistemas: o Nitrogênio substitucional e a vacância simples. Para o Nitrogênio, analisamos as possíveis distorções associadas a este centro, procurando interpretar os resultados experimentais. A vacância simples mostrou-se ser um sistema bastante semelhante à vacância simples em Silício: em ambos os casos observa - se uma distorção Jahn-Teller. O modelo adotado mostrou- se capaz de descrever satisfatoriamente as estruturas eletrônicas dos dois centros estudados...

Research paper thumbnail of Structural and electronic properties of vacancies and impurities in non-passivated silicon nanowires by first-principles calculations

Proceedings of Brazilian Workshop on Semiconductor Physics

In this work, we report our preliminary results for the presence of the vacancy, as well as for t... more In this work, we report our preliminary results for the presence of the vacancy, as well as for the boron and nitrogen impurities in non-passivated [001] silicon nanowires. The results show that defects and dopants tend to segregate to the nanowire surfaces, as observed for passivated [110] ones, but at the (-2) charge state, due to the metallic character of the [001] nanowire. The vacancies are stable at the facets, while the impurities stay preferentially at the interstitial site, making bridges with the lateral surface Si atoms, below to this surface. As a consequence, the surface -states located at the facets are filled and a small bandgap appears in the calculated defect band structures.

Research paper thumbnail of Molecular Signature in the Photoluminescence of α-Glycine, L-Alanine and L-Asparagine Crystals: Detection, ab initio Calculations, and Bio-sensor Applications

AIP Conference Proceedings

We present the photoluminescence spectra of α-glycine, L-alanine, and L-asparagine crystals. They... more We present the photoluminescence spectra of α-glycine, L-alanine, and L-asparagine crystals. They are broad and structured, comprising green to ultraviolet emission in the 1.75–3.60 eV range. Absorption measurements show that the band gap energies of the crystals are of the order of 5.0 eV. Ab initio calculations of their electronic structures allow for the assignment of the observed peaks in the visible region to lattice-related processes of exciton nature associated with polaron levels. The very thin photoluminescence peaks in the ultraviolet region are assigned to intramolecular transitions, being a signature of the weakly interacting amino acid molecules in the crystals.

Research paper thumbnail of Ab initio Results for the Structural and Electronic Properties of Intrinsic Defects in PbTe

In this work, we have performed spin-polarized calculations for the structural and electronic pro... more In this work, we have performed spin-polarized calculations for the structural and electronic properties of vacancies and anti-site defects in the rocksalt PbTe. Our obtained results have shown that both the Pb and Te antisites are the favorable defects in Pb and Te rich conditions, respectively. Moreover, in the perfect stoichiometry condition, the antisites, as well as the Te vacancy, are equally probable to find. Considering the charge injection in the system, all the defects change from the 2+ charge state to the 2one within 14 meV, at around 80 meV from the valence band edge within the bandgap. This feature makes it difficult to experimentally characterize these defects in PbTe.

Research paper thumbnail of Obtaining the magnetic susceptibility of the heme complex from DFT calculations

AIP Advances

Magnetic field interactions with particles, as observed in magnetophoresis, are becoming importan... more Magnetic field interactions with particles, as observed in magnetophoresis, are becoming important tool to understand the nature of the iron role in heme molecular complex, besides other useful applications. Accurate estimations of some macroscopic magnetic properties from quantum mechanical calculations, such as the magnetic susceptibility, can also check the reliability of the heme microscopic models. In this work we report, by using the Stoner criterion, a simple way to obtain the magnetic susceptibility of the heme complex from Density Functional Theory calculations. Some of our calculated structural properties and electronic structure show good agreement with both the available experimental and theoretical data, and the results show that its groundstate is a triplet 3 A state. From the obtained results, we have evaluated the exchange interaction energy, J = 0.98 eV, the associated magnetic energy gain, ∆E M = −0.68 eV, and the magnetic susceptibility, χ 0 = 1.73 × 10 −6 cm 3 /mol for the heme alone (with uncompleted Fe ligands). If we consider the heme complex with the two histidine residues (completing the Fe ligands), we have then obtained χ 0 = 5.27 × 10 −12 cm 3 /g, which is in good agreement with experimental magnetophoresis data.

Research paper thumbnail of Structural and Electronic Properties of Vacancies and Impurities in non- passivated Silicon Nanowires by first-principles calculations

18TH BRAZILIAN WORKSHOP ON SEMICONDUCTOR PHYSICS, 2017

In this work, we report our preliminary results for the presence of the vacancy, as well as for t... more In this work, we report our preliminary results for the presence of the vacancy, as well as for the boron and nitrogen impurities in non-passivated [001] silicon nanowires. The results show that defects and dopants tend to segregate to the nanowire surfaces, as observed for passivated [110] ones, but at the (-2) charge state, due to the metallic character of the [001] nanowire. The vacancies are stable at the facets, while the impurities stay preferentially at the interstitial site, making bridges with the lateral surface Si atoms, below to this surface. As a consequence, the surface -states located at the facets are filled and a small bandgap appears in the calculated defect band structures.

Research paper thumbnail of Theoretical study of Sn and Te adsorption over graphene from ab initio calculations

AIP Advances

In this work, we report on theoretical calculations for the adsorption of both Sn and Te atoms ov... more In this work, we report on theoretical calculations for the adsorption of both Sn and Te atoms over a graphene monolayer. Our obtained results show that Sn is chemisorbed over a graphene CC bond, once the presence of Sn over the substrate changes some of graphene's CC sp 2-like bond character to a more covalently reactive sp 3-like one. On the other hand, Te is physisorbed over a C atom of the graphene sheet, since it is weakly connected to the surface atoms by van der Waals' forces. However, both Sn and Te are extremely mobile over the graphene monolayer because the energy barriers between the adsorption sites are very small. Considering that SiC surfaces passivated with graphene enhance the strength of the C-Sn bonds in the MBE growth procedure, our results, theoretically, confirm the growth of a SnTe layer on graphene.

Research paper thumbnail of Interplay between magnetic, metal/insulator and topological phases in Hg1-xMnxTe alloys: prediction of a ferromagnetic Weyl semimetal at x= 0.25

Journal of Physics: Condensed Matter

Research paper thumbnail of Vibrational properties of cubic Inx Ga1-xN structures

Research paper thumbnail of Structural, electronic, and optical properties of ZrO2 from ab initio calculations

Journal of Applied Physics, 2006

Structural, electronic, and optical properties for the cubic, tetragonal, and monoclinic crystall... more Structural, electronic, and optical properties for the cubic, tetragonal, and monoclinic crystalline phases of ZrO2, as derived from ab initio full-relativistic calculations, are presented. The electronic structure calculations were carried out by means of the all-electron full-potential linear augmented plane wave method, within the framework of the density functional theory and the local density approximation. The calculated carrier effective masses

Research paper thumbnail of Molecular Signature in the Photoluminescence of alpha-Glycine, L-Alanine and L-Asparagine Crystals: Detection, ab initio Calculations, and Biosensor Applications

We present the photoluminescence spectra of alpha-glycine, L-alanine, and L-asparagine crystals. ... more We present the photoluminescence spectra of alpha-glycine, L-alanine, and L-asparagine crystals. They are broad and structured, comprising green to ultraviolet emission in the 1.75-3.60 eV range. Absorption measurements show that the band gap energies of the crystals are of the order of 5.0 eV. Ab initio calculations of their electronic structures allow for the assignment of the observed peaks in

Research paper thumbnail of Structural and Electronic Properties of Vacancies and Impurities in non- passivated Silicon Nanowires by first-principles calculations

18TH BRAZILIAN WORKSHOP ON SEMICONDUCTOR PHYSICS, 2017

In this work, we report our preliminary results for the presence of the vacancy, as well as for t... more In this work, we report our preliminary results for the presence of the vacancy, as well as for the boron and nitrogen impurities in non-passivated [001] silicon nanowires. The results show that defects and dopants tend to segregate to the nanowire surfaces, as observed for passivated [110] ones, but at the (-2) charge state, due to the metallic character of the [001] nanowire. The vacancies are stable at the facets, while the impurities stay preferentially at the interstitial site, making bridges with the lateral surface Si atoms, below to this surface. As a consequence, the surface -states located at the facets are filled and a small bandgap appears in the calculated defect band structures.

Research paper thumbnail of Ab initio Results for the Structural and Electronic Properties of Intrinsic Defects in PbTe

18TH BRAZILIAN WORKSHOP ON SEMICONDUCTOR PHYSICS, 2017

In this work, we have performed spin-polarized calculations for the structural and electronic pro... more In this work, we have performed spin-polarized calculations for the structural and electronic properties of vacancies and anti-site defects in the rocksalt PbTe. Our obtained results have shown that both the Pb and Te antisites are the favorable defects in Pb and Te rich conditions, respectively. Moreover, in the perfect stoichiometry condition, the anti-sites, as well as the Te vacancy, are equally probable to find. Considering the charge injection in the system, all the defects change from the 2+ charge state to the 2-one within 14 meV, at around 80 meV from the valence band edge within the bandgap. This feature makes it difficult to experimentally characterize these defects in PbTe.

Research paper thumbnail of Obtaining the magnetic susceptibility of the heme complex from DFT calculations

Magnetic field interactions with particles, as observed in magnetophoresis, are becoming importan... more Magnetic field interactions with particles, as observed in magnetophoresis, are becoming important tool to understand the nature of the iron role in heme molecular complex, besides other useful applications. Accurate estimations of some macroscopic magnetic properties from quantum mechanical calculations, such as the magnetic susceptibility , can also check the reliability of the heme microscopic models. In this work we report, by using the Stoner criterion, a simple way to obtain the magnetic susceptibility of the heme complex from Density Functional Theory calculations. Some of our calculated structural properties and electronic structure show good agreement with both the available experimental and theoretical data, and the results show that its groundstate is a triplet 3 A state. From the obtained results, we have evaluated the exchange interaction energy, J = 0.98 eV, the associated magnetic energy gain, ∆E M = −0.68 eV, and the magnetic susceptibility, χ 0 = 1.73 × 10 −6 cm 3 /mol for the heme alone (with uncompleted Fe ligands). If we consider the heme complex with the two histidine residues (completing the Fe ligands), we have then obtained χ 0 = 5.27 × 10 −12 cm 3 /g, which is in good agreement with experimental magnetophoresis data. © 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license

Research paper thumbnail of Structural, electronic, vibrational, and dielectric properties of LaBGeO5 from first principles

Journal of Applied Physics, 2014

Research paper thumbnail of Ab initio calculation of the dynamical properties of GaAs and GaN (110) and (100) surfaces

Journal of Physics Conference Series

In this work, we have calculated the vibrational modes and frequencies of the crystalline PPP (in... more In this work, we have calculated the vibrational modes and frequencies of the crystalline PPP (in both the Pbam and Pnnm symmetries) and PPV (in the P2 1 /c symmetry). Our results are in good agreement with the available experimental data. Also, we have calculated the temperature dependence of their specific heats at constant volume, and of their vibrational entropies. Based on our results, at high temperatures, the PPP is more stable in the Pnnm structure than in the Pbam

Research paper thumbnail of Níveis profundos associados a vacância e nitrogênio em diamante

Research paper thumbnail of Interchain Effects on the Vibrational Properties of PPP and PPV

AIP Conference Proceedings

In this work, we have calculated the vibrational modes of the poly-paraphenylene (PPP) in both Pb... more In this work, we have calculated the vibrational modes of the poly-paraphenylene (PPP) in both Pbam and Pnnm structures, and of the poly-paraphenylene-vinylene (PPV) in the P2 1 /c structure. Our results agree well (within 3 % of error) with the available experimental data, whenever these comparison is possible. Based on our calculations, we show that the acoustical longitudinal mode stretches the π-bonds, while the acoustical transversal ones leads only to their torsion.

Research paper thumbnail of Electronic Structure of Point Defects in SiC

Brazilian Journal of Physics

In this work we h a ve calculated the electronic structure of point defects in cubic silicon carb... more In this work we h a ve calculated the electronic structure of point defects in cubic silicon carbide(3C-SiC) using the Molecular Cluster Model within the framework of the ab initio LCAO-MO Unrestricted Hartree-Fock method. The following point defects were studied: vacancies, anti-sites, Si and C interstitials at both tetrahedral and hexagonal sites. Our results show good agreement with both experimental and other theoretical calcula-tions. From the total energy evaluation, without including relaxation and/or local distortion eeects, we found that carbon anti-site and silicon vacancy are the most energetically stable point defects in both C-rich and stoichiometrically 3C-SiC, while for Si-rich material, silicon anti-site and carbon vacancy are the most stable ones.

Research paper thumbnail of Thermoelectric properties of IV–VI-based heterostructures and superlattices

Journal of Solid State Chemistry

Doping in a manner that introduces anisotropy in order to reduce thermal conductivity is a signif... more Doping in a manner that introduces anisotropy in order to reduce thermal conductivity is a significant focus in thermoelectric research today. By solving the semiclassical Boltzmann transport equations in the constant scattering time (τ) approximation, in conjunction with ab initio electronic structure calculations, within Density Functional Theory, we compare the Seebeck coefficient (S) and figure of merit (ZT) of bulk PbTe to PbTe/SnTe/PbTe heterostructures and PbTe doping superlattices (SLs) with periodically doped planes. Bismuth and Thallium were used as the n- and p-type impurities, respectively. The effects of carrier concentration are considered via chemical potential variation in a rigid band approximation. The impurity bands near the Fermi level in the electronic structure of PbTe SLs are of Tl s- and Bi p-character, and this feature is independent of the doping concentration or the distance between impurity planes. We observe the impurity bands to have a metallic nature i...