Rafael Gonzalez-Hernandez | Universidad del Norte - Barranquilla, Colombia (original) (raw)
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Papers by Rafael Gonzalez-Hernandez
Physica B: Condensed Matter, 2010
RTAsO (R=rare-earth and T=transition metals) compounds have been studied using density functional... more RTAsO (R=rare-earth and T=transition metals) compounds have been studied using density functional theory with the local spin-density approximation (LSDA). In order to take into account the strong on-site Coulomb interaction U present in RTAsO, we have also performed the LSDA+U calculations. We investigated the electronic structure with on-site Coulomb potential for the R-derived 4f and T-derived 3d orbitals to obtain the correct ground state of RTAsO. The structural parameters, band structures and density of states have been given in detail. Overall, the technique developed and tested in this work holds promise in enabling accurate and fully predictive calculations of strongly correlated electron materials. A detailed analysis shows that the LSDA+U method provides the better description of our systems. We note that there is no ab-initio study related to these materials.
Applied Surface Science, 2014
ABSTRACT A comparative analysis of the geometry and the electronic characteristics of nonpolar Ga... more ABSTRACT A comparative analysis of the geometry and the electronic characteristics of nonpolar GaN surfaceswas carried out using density-functional theory (DFT) with different approximations for the exchange-correlation energy (LDA, PBE, PBEsol, RPBE, TPSS, revTPSS, and HSE). The obtained data show that theGaN(1 0¯1 0) (m-plane) is more energetically stable than the GaN(1 1¯2 0) (a-plane) surface. However,these surfaces have similar surface relaxation geometry, with a Ga-N surface bond-length contraction ofaround 6–7% and a Ga-N surface rotational angle in the range of 6–9◦. Our results show that the use ofdifferent exchange-correlation functionals does not significantly change the surface energy and surfacegeometry. In addition, we found the presence of surface intra-gap states that reduce the band gap of thenonpolar GaN surface with respect to the bulk value, in agreement with recent photoelectron and surfaceoptical spectroscopy experiments.
Computational Materials Science, 2014
ABSTRACT We carried out first-principles calculations in order to provide comprehensive informati... more ABSTRACT We carried out first-principles calculations in order to provide comprehensive information regarding the nitrogen vacancy effects (N-v) on the magnetism of NixAl1-xN(x = 0.028) system. It has been found that the system is energetically more favorable for single Ni doping in Al site with one N-vacancy when compared to single Ni doping configuration. The present calculation reveals a stable ferromagnetism in Ni-doped wurtzite AlN with a magnetic moment of 3.00 mu(B), for 2.8% of Ni doping. When Ni is substituted in Al site with N-vacancy the system becomes half-metallic. The N-vacancy induced defects also show a lower magnetic moment than 3.00 mu(B), which is in good agreement with the experimental observations. The results indicate that magnetic moment is reduced by the weak 3d-3d spin coupling due to the long range hybridization between Ni-3d and N defect states.
Computational Materials Science, 2014
ABSTRACT We have carried out first-principles total-energy calculations in order to study the ele... more ABSTRACT We have carried out first-principles total-energy calculations in order to study the electronic structure and thermodynamic properties of In1�xBxP semiconducting alloys using the GGA and LDA formalisms within density functional theory (DFT) with a plane-wave ultrasoft pseudopotential scheme. We have also taken into account the correlation effects of the 3d-In orbitals within the LDA+U method to calculate the band-gap energy. We use special quasirandom structures to investigate the effect of the substituent concentration on structural parameter, band gap energy, mixing enthalpy and phase diagram of In1�xBxP alloys for x = 0, 0.25, 0.50, 0.75 and 1. It is found that the lattice parameters of the In1�xBxP alloys decrease with B-concentration, showing a negative deviation from Vegard’s law, while the bulk modulus increases with composition x, showing a large deviation from the linear concentration dependence (LCD). The calculated band structure presents a similar behavior for any B-composition using LDA, PBE or LDA+U approach. Our results predict that the band-gap shows a x-dependent nonlinear behavior. Calculated band gaps also shows a transition from (Gamma-Gamma)-direct to (Gamma-Delta)-indirect at x = 0.611 and 0.566 for LDA and PBE functionals, respectively. Our calculations predict that the In1-�xBxP alloy to be stable at unusual high temperature for both LDA and PBE potentials.
Physical Review B, 2009
This paper was published online on 26 February 2009 with errors in the title. The title of the ar... more This paper was published online on 26 February 2009 with errors in the title. The title of the article should read as “First-principles study of H ordering in the α phase of MH systems (M= Sc, Y, Ti, Zr)”. The paper has been corrected as of 19 March 2009. The title is incorrect in ...
physica status solidi (b), 2009
Journal of Physics and Chemistry of Solids, 2013
ABSTRACT We discuss the energetic stability and electronic structure of zirconium adsorption and ... more ABSTRACT We discuss the energetic stability and electronic structure of zirconium adsorption and incorporation on a 2×2 reconstructed AlN(0001) surface. We employ density-functional theory within the generalized-gradient approximation to study such effects. First-principles total energy calculations reveal that the most stable positions of a Zr adatom on the reconstructed 2×2-T4 AlN(0001) surface are at the S1 and Sp substitutional sites. In addition, calculating the relative surface energy of several configurations, we constructed a phase diagram showing the energetically most stable surfaces as a function of the aluminium chemical potential. Based on these results, we find that incorporation at Al-substitutional sites is energetically favorable compared to adsorption on the top layers. In particular, we find that Zr-S1 and Zr-Sp structures are stable over the entire chemical potential range. This effect can lead to the formation of a non-reactive interfacial ZrN(111) layer on the AlN(0001) surface, which can offer a good interfacial combination between AlN substrate and other metal contacts, i.e. zirconium.
Journal of Alloys and Compounds, 2013
ABSTRACT Using first-principles total-energy calculations, we investigate the structural, electro... more ABSTRACT Using first-principles total-energy calculations, we investigate the structural, electronic and thermodynamic properties of the cubic Sc1−xInxP semiconducting alloys. The calculations are based on the full-potential linearized-augmented plane wave (FP-LAPW) method within density functional theory (DFT). The exchange–correlation effect is treated by both local-density approximation (LDA) and generalized-gradient approximation (GGA). In the latter approach, both Perdew-Burke-Ernzerhof (PBE) and EngelVosko (EV) functional of the exchange–correlation energy were used. The effect of atomic composition on structural parameters, band-gap energy, mixing enthalpy and phase diagram was analyzed for x = 0, 0.25, 0.5, 0.75, 1. Lattice constant, bulk modulus, and band-gap energy for zinc-blende Sc1−xInxP alloys show nonlinear dependence on the aluminium composition x. Deviations of the lattice constant from Vegard’s law, and deviations of the bulk modulus and band-gap energy from linear concentration dependence (LCD) were found. The variation of the calculated equilibrium lattice constant versus indium concentration shows a small deviation from Vegard’s law with upward bowing parameter of −0.043 Å and −0.058 Å for PBE and LDA, respectively. The bulk modulus as a function of indium composition shows a small deviation from the linear concentration dependence (LCD) with upward bowing equal to −0.790 GPa using PBE, and with net downward bowing of 0.847 GPa using LDA. The results show that the band gap undergoes a direct (X → X)-to-direct (Γ → Γ) transition at a given indium composition x. The physical origin of the band-gap bowing in zinc-blende Sc1−xInxP semiconducting alloys was investigated. The calculated excess mixing enthalpy is positive over the entire indium composition range.
International Journal of Quantum Chemistry, 2013
ABSTRACT We have performed spin-polarized first-principles calculations to explore the vanadium a... more ABSTRACT We have performed spin-polarized first-principles calculations to explore the vanadium adsorption and diffusion on the AlN(0001)-(2 × 2) surface. The calculations were performed using the generalized gradient approximation with ultrasoft pseudopotential within the density functional theory. The surface is modeled using the repeated slabs approach. To study the most favorable reconstruction with vanadium adatom, we considered H3, T4, and T1 high-symmetry sites. We found that the most energetically favorable structure corresponds to the V-T4 reconstruction or the vanadium adatom located at the hcp-hollow (T4) site whereas the vanadium adsorption on-top of a aluminium atom (T1 position) is energetically unfavorable. The vanadium diffusion on surface shows an activation energy of 0.262 eV (T4–H3). The resultant reconstruction of the vanadium adsorption on AlN(0001)-(2 ×2) surface presents a lateral relaxation of some hundredth of Å in the most stable site. The comparison between the density of states of the AlN(0001) clean surface and with vanadium adatom is also examined. © 2012 Wiley Periodicals, Inc.
International Journal of Hydrogen Energy, 2008
Sc Y La H HYFUSEN 2007 a b s t r a c t In this work the electronic behavior of hydrogen impuritie... more Sc Y La H HYFUSEN 2007 a b s t r a c t In this work the electronic behavior of hydrogen impurities in lanthanum (La), scandium (Sc) and yttrium (Y) matrices is studied. For each one of the systems some fundamental physical properties are determined, as the induced screening electron density, the volume of solution of hydrogen, the solution heat and the variation of the density of electronic states, using the formalism of the density functional theory (DFT) and the Jellium model. We propose a new parameterization for the solution heat in terms of the change of total energy of the system, obtaining an excellent agreement with experimental values reported in the literature. One of the main features of this model is that it yields accurate values of those properties of the system which are strongly dependent on the density of free electrons. The results obtained by this method are compared with experimental data available in the literature, as well as with more sophisticated theoretical models.
Applied Surface Science, 2013
ABSTRACT We have performed first-principles calculations of energetic stability and electronic st... more ABSTRACT We have performed first-principles calculations of energetic stability and electronic structure of nickel adsorption and incorporation on a 2 × 2 reconstructed GaN(0 0 0 1) surface. Our total energy results show that the most stable positions of a Ni adatom on the reconstructed 2 × 2-T4 GaN(0 0 0 1) surface are at the H3a0 and T4 adsorption sites. We found that the Ni adatom diffusion energy barrier between the H3a0 and T4 sites is around 0.16 eV, which is an indication of a significant Ni adatom diffusion on this surface. In addition, calculating the relative surface energy of several configurations, we constructed a phase diagram showing the energetically most stable surfaces as a function of the Ga chemical potential. Based on these results, we found that Ni adsorption is energetically more favorable compared with Ni incorporation in the Ga-substitutional and interstitial sites. In addition, confirming previous experimental results, we found that the growth of NiGax and Ni monolayers on the GaN(0 0 0 1) surface is possible.
Physica B: Condensed Matter, 2010
RTAsO (R=rare-earth and T=transition metals) compounds have been studied using density functional... more RTAsO (R=rare-earth and T=transition metals) compounds have been studied using density functional theory with the local spin-density approximation (LSDA). In order to take into account the strong on-site Coulomb interaction U present in RTAsO, we have also performed the LSDA+U calculations. We investigated the electronic structure with on-site Coulomb potential for the R-derived 4f and T-derived 3d orbitals to obtain the correct ground state of RTAsO. The structural parameters, band structures and density of states have been given in detail. Overall, the technique developed and tested in this work holds promise in enabling accurate and fully predictive calculations of strongly correlated electron materials. A detailed analysis shows that the LSDA+U method provides the better description of our systems. We note that there is no ab-initio study related to these materials.
Applied Surface Science, 2014
ABSTRACT A comparative analysis of the geometry and the electronic characteristics of nonpolar Ga... more ABSTRACT A comparative analysis of the geometry and the electronic characteristics of nonpolar GaN surfaceswas carried out using density-functional theory (DFT) with different approximations for the exchange-correlation energy (LDA, PBE, PBEsol, RPBE, TPSS, revTPSS, and HSE). The obtained data show that theGaN(1 0¯1 0) (m-plane) is more energetically stable than the GaN(1 1¯2 0) (a-plane) surface. However,these surfaces have similar surface relaxation geometry, with a Ga-N surface bond-length contraction ofaround 6–7% and a Ga-N surface rotational angle in the range of 6–9◦. Our results show that the use ofdifferent exchange-correlation functionals does not significantly change the surface energy and surfacegeometry. In addition, we found the presence of surface intra-gap states that reduce the band gap of thenonpolar GaN surface with respect to the bulk value, in agreement with recent photoelectron and surfaceoptical spectroscopy experiments.
Computational Materials Science, 2014
ABSTRACT We carried out first-principles calculations in order to provide comprehensive informati... more ABSTRACT We carried out first-principles calculations in order to provide comprehensive information regarding the nitrogen vacancy effects (N-v) on the magnetism of NixAl1-xN(x = 0.028) system. It has been found that the system is energetically more favorable for single Ni doping in Al site with one N-vacancy when compared to single Ni doping configuration. The present calculation reveals a stable ferromagnetism in Ni-doped wurtzite AlN with a magnetic moment of 3.00 mu(B), for 2.8% of Ni doping. When Ni is substituted in Al site with N-vacancy the system becomes half-metallic. The N-vacancy induced defects also show a lower magnetic moment than 3.00 mu(B), which is in good agreement with the experimental observations. The results indicate that magnetic moment is reduced by the weak 3d-3d spin coupling due to the long range hybridization between Ni-3d and N defect states.
Computational Materials Science, 2014
ABSTRACT We have carried out first-principles total-energy calculations in order to study the ele... more ABSTRACT We have carried out first-principles total-energy calculations in order to study the electronic structure and thermodynamic properties of In1�xBxP semiconducting alloys using the GGA and LDA formalisms within density functional theory (DFT) with a plane-wave ultrasoft pseudopotential scheme. We have also taken into account the correlation effects of the 3d-In orbitals within the LDA+U method to calculate the band-gap energy. We use special quasirandom structures to investigate the effect of the substituent concentration on structural parameter, band gap energy, mixing enthalpy and phase diagram of In1�xBxP alloys for x = 0, 0.25, 0.50, 0.75 and 1. It is found that the lattice parameters of the In1�xBxP alloys decrease with B-concentration, showing a negative deviation from Vegard’s law, while the bulk modulus increases with composition x, showing a large deviation from the linear concentration dependence (LCD). The calculated band structure presents a similar behavior for any B-composition using LDA, PBE or LDA+U approach. Our results predict that the band-gap shows a x-dependent nonlinear behavior. Calculated band gaps also shows a transition from (Gamma-Gamma)-direct to (Gamma-Delta)-indirect at x = 0.611 and 0.566 for LDA and PBE functionals, respectively. Our calculations predict that the In1-�xBxP alloy to be stable at unusual high temperature for both LDA and PBE potentials.
Physical Review B, 2009
This paper was published online on 26 February 2009 with errors in the title. The title of the ar... more This paper was published online on 26 February 2009 with errors in the title. The title of the article should read as “First-principles study of H ordering in the α phase of MH systems (M= Sc, Y, Ti, Zr)”. The paper has been corrected as of 19 March 2009. The title is incorrect in ...
physica status solidi (b), 2009
Journal of Physics and Chemistry of Solids, 2013
ABSTRACT We discuss the energetic stability and electronic structure of zirconium adsorption and ... more ABSTRACT We discuss the energetic stability and electronic structure of zirconium adsorption and incorporation on a 2×2 reconstructed AlN(0001) surface. We employ density-functional theory within the generalized-gradient approximation to study such effects. First-principles total energy calculations reveal that the most stable positions of a Zr adatom on the reconstructed 2×2-T4 AlN(0001) surface are at the S1 and Sp substitutional sites. In addition, calculating the relative surface energy of several configurations, we constructed a phase diagram showing the energetically most stable surfaces as a function of the aluminium chemical potential. Based on these results, we find that incorporation at Al-substitutional sites is energetically favorable compared to adsorption on the top layers. In particular, we find that Zr-S1 and Zr-Sp structures are stable over the entire chemical potential range. This effect can lead to the formation of a non-reactive interfacial ZrN(111) layer on the AlN(0001) surface, which can offer a good interfacial combination between AlN substrate and other metal contacts, i.e. zirconium.
Journal of Alloys and Compounds, 2013
ABSTRACT Using first-principles total-energy calculations, we investigate the structural, electro... more ABSTRACT Using first-principles total-energy calculations, we investigate the structural, electronic and thermodynamic properties of the cubic Sc1−xInxP semiconducting alloys. The calculations are based on the full-potential linearized-augmented plane wave (FP-LAPW) method within density functional theory (DFT). The exchange–correlation effect is treated by both local-density approximation (LDA) and generalized-gradient approximation (GGA). In the latter approach, both Perdew-Burke-Ernzerhof (PBE) and EngelVosko (EV) functional of the exchange–correlation energy were used. The effect of atomic composition on structural parameters, band-gap energy, mixing enthalpy and phase diagram was analyzed for x = 0, 0.25, 0.5, 0.75, 1. Lattice constant, bulk modulus, and band-gap energy for zinc-blende Sc1−xInxP alloys show nonlinear dependence on the aluminium composition x. Deviations of the lattice constant from Vegard’s law, and deviations of the bulk modulus and band-gap energy from linear concentration dependence (LCD) were found. The variation of the calculated equilibrium lattice constant versus indium concentration shows a small deviation from Vegard’s law with upward bowing parameter of −0.043 Å and −0.058 Å for PBE and LDA, respectively. The bulk modulus as a function of indium composition shows a small deviation from the linear concentration dependence (LCD) with upward bowing equal to −0.790 GPa using PBE, and with net downward bowing of 0.847 GPa using LDA. The results show that the band gap undergoes a direct (X → X)-to-direct (Γ → Γ) transition at a given indium composition x. The physical origin of the band-gap bowing in zinc-blende Sc1−xInxP semiconducting alloys was investigated. The calculated excess mixing enthalpy is positive over the entire indium composition range.
International Journal of Quantum Chemistry, 2013
ABSTRACT We have performed spin-polarized first-principles calculations to explore the vanadium a... more ABSTRACT We have performed spin-polarized first-principles calculations to explore the vanadium adsorption and diffusion on the AlN(0001)-(2 × 2) surface. The calculations were performed using the generalized gradient approximation with ultrasoft pseudopotential within the density functional theory. The surface is modeled using the repeated slabs approach. To study the most favorable reconstruction with vanadium adatom, we considered H3, T4, and T1 high-symmetry sites. We found that the most energetically favorable structure corresponds to the V-T4 reconstruction or the vanadium adatom located at the hcp-hollow (T4) site whereas the vanadium adsorption on-top of a aluminium atom (T1 position) is energetically unfavorable. The vanadium diffusion on surface shows an activation energy of 0.262 eV (T4–H3). The resultant reconstruction of the vanadium adsorption on AlN(0001)-(2 ×2) surface presents a lateral relaxation of some hundredth of Å in the most stable site. The comparison between the density of states of the AlN(0001) clean surface and with vanadium adatom is also examined. © 2012 Wiley Periodicals, Inc.
International Journal of Hydrogen Energy, 2008
Sc Y La H HYFUSEN 2007 a b s t r a c t In this work the electronic behavior of hydrogen impuritie... more Sc Y La H HYFUSEN 2007 a b s t r a c t In this work the electronic behavior of hydrogen impurities in lanthanum (La), scandium (Sc) and yttrium (Y) matrices is studied. For each one of the systems some fundamental physical properties are determined, as the induced screening electron density, the volume of solution of hydrogen, the solution heat and the variation of the density of electronic states, using the formalism of the density functional theory (DFT) and the Jellium model. We propose a new parameterization for the solution heat in terms of the change of total energy of the system, obtaining an excellent agreement with experimental values reported in the literature. One of the main features of this model is that it yields accurate values of those properties of the system which are strongly dependent on the density of free electrons. The results obtained by this method are compared with experimental data available in the literature, as well as with more sophisticated theoretical models.
Applied Surface Science, 2013
ABSTRACT We have performed first-principles calculations of energetic stability and electronic st... more ABSTRACT We have performed first-principles calculations of energetic stability and electronic structure of nickel adsorption and incorporation on a 2 × 2 reconstructed GaN(0 0 0 1) surface. Our total energy results show that the most stable positions of a Ni adatom on the reconstructed 2 × 2-T4 GaN(0 0 0 1) surface are at the H3a0 and T4 adsorption sites. We found that the Ni adatom diffusion energy barrier between the H3a0 and T4 sites is around 0.16 eV, which is an indication of a significant Ni adatom diffusion on this surface. In addition, calculating the relative surface energy of several configurations, we constructed a phase diagram showing the energetically most stable surfaces as a function of the Ga chemical potential. Based on these results, we found that Ni adsorption is energetically more favorable compared with Ni incorporation in the Ga-substitutional and interstitial sites. In addition, confirming previous experimental results, we found that the growth of NiGax and Ni monolayers on the GaN(0 0 0 1) surface is possible.