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Papers by William Lopez Perez

Research paper thumbnail of Estudios AB-INITIO de las propiedades estructurales y electrónicas del nitruro de vanadio

Ciencia e Ingeniería Neogranadina, 2007

En este estudio se presentan las propiedades estructurales y electrónicas del compueston nitruro ... more En este estudio se presentan las propiedades estructurales y electrónicas del compueston nitruro de vanadio VN en las estructuras cloruro de sodio (NaCl), cloruro de cesio (CsCl), blenda de zinc (ZnBl) y wurzita usando cálculos de primeros principios o ab-initio. Se encontró que la fase NaCl es la estructura de cristalización más estable para este compuesto, con parámetro de red a=4.12 A y módulo de volumen Bo= 305 GPa. Los cálculos se realizaron en el marco de la Teoría del Funcional Densidad (DFT), usando el método de Ondas Planas Aumentadas y Linealizadas (FP-LAPW). Los efectos de intercambio y correlación se trataron dentro de la Aproximación del Gradiente Generalizado (GGA), implementada en el método Perdew-Burke-Ernzerhof (PBE).

Research paper thumbnail of Pressure effect on electronic properties of Sc 0.5 In 0.5 N compound

physica status solidi (b), 2009

Research paper thumbnail of Pressure effects on the electronic and magnetic properties of GaxV1−xN compounds: Ab-initio study

Materials Science and Engineering: B, 2009

We report an ab-initio study of the pressure effects on the electronic and the magnetic propertie... more We report an ab-initio study of the pressure effects on the electronic and the magnetic properties of Ga x V 1−x N compounds (x = 0.25, 0.50 and 0.75) in wurtzite-derived structures. We use the full-potential linearized augmented plane wave plus local orbitals method (LAPW + lo) within of the spin density functional theory framework. The lattice constant is found to vary linearly with Ga-concentration. The magnetic moment changes for a critical pressure. At x = 0.75, a rather abrupt onset of the magnetic moment from 0 to 2 B at P cr ∼22.8 GPa is observed. For x = 0.25 and 0.50 Ga concentrations, the magnetic moment increases gradually when the pressure decreases toward the equilibrium value. We study the transition pressure dependence to a ferromagnetic phase near the onset of magnetic moment for each Ga x V 1−x N compounds. The calculation of the density of states with Ga concentration is carried out considering two spin polarizations. The results reveal that for x = 0.75 the compound behaves as a conductor for the spin-up polarization and that the density of states for spin-down polarization is zero at the Fermi level. At this concentration the compound presents a half metallic behavior; therefore this material could be potentially useful as spin injector. At high pressures P > P cr the compounds exhibit a metallic behavior.

Research paper thumbnail of Electronic structure and magnetism in : An ab initio study

Journal of Magnetism and Magnetic Materials, 2009

We carry out first principles spin polarized calculations in order to study the electronic struct... more We carry out first principles spin polarized calculations in order to study the electronic structure and magnetism of Ni 0:0625 Zn 0:9375 O compound using density functional theory (DFT) within a plane-wave ultrasoft pseudopotential scheme. The electronic properties of Ni x Zn 1Àx O at a concentration of 6.25% are analyzed using a 2 Â 2 Â 2 wurtzite ZnO supercell. We optimize the lattice constants of ZnO pure and Ni 0:0625 Zn 0:9375 O. We observe that if one Zn atom is substituted by one Ni atom in the wurtzite ZnO supercell, the lattice parameters decrease slightly some thousandths of angstrom. We also find a stable ferromagnetic state in Ni doped ZnO with a total magnetization of 2:04 m B per supercell. Using the optimized lattice parameters, we have calculated the band structure and density of states of Ni 0:0625 Zn 0:9375 O.

Research paper thumbnail of Barrera de Difusión de un Adsorbato Atómico Sobre la Superficie Bn (0001)-2x2 en Estructura Wurzita

ABSTRACT We have carried out total energy calculations to study the Boron or Nitrogen adsorption ... more ABSTRACT We have carried out total energy calculations to study the Boron or Nitrogen adsorption on w-BN(0001)-2x2 surface. In the calculations, the Konh-Sham equations are solved with the plane wave basis and atomic pseudopotentials using General-ized Gradient Approximation (GGA) for the exchange-correlations potential. We consider the T1, T4 y H3 especial points in order to obtain the more stable reconstruction. We predict that B-T4 y N-H3 structures are the most energetically favorable for rich Boron and Nitrogen configurations, respectively. We find that the atomic adsorption on top of a Boron atom in the surface (site T1) is completely unfavorable. For the Nitrogen adatom we obtained a diffusion barrier of 1,083 eV, while for the Boron adatom was 2.09 eV. Hemos realizado cálculos de energía total para estudiar la adsorción de un átomo de Boro o Nitrógeno sobre la superficie (0001) del w-BN en una geometría 2x2. En los cálculos, se resuelven las ecuaciones de Konh-Sham con una base de ondas planas y pseudopotenciales atómicos, y usando la aproximación de gradiente generali-zado para describir los efectos de intercambio y correlación. Para obtener la reconstrucción más estable consi-deramos los puntos especiales T1, T4 y H3. Predecimos que las estructuras B-T4 y N-H3 son las más favorables energéticamente para configuraciones ricas en Boro y Nitrógeno, respectivamente. Encontramos que la adsor-ción atómica sobre un átomo de Boro de la superficie (sitio T1) es completamente desfavorable. Para el adsor-bato Nitrógeno obtuvimos una barrera de difusión de 1.083 eV, mientras que para el Boro la energía de barrera es de 2.09 eV.

Research paper thumbnail of Estudio de la Superred 1x1-(0001) GaN/RuN, Usando el Método Ondas Planas Aumentadas y Linealizadas con la Teoría del Funcional de la Densidad

ABSTRACT We report a study of the structural and electronic properties of short-period wurtzite 1... more ABSTRACT We report a study of the structural and electronic properties of short-period wurtzite 1x1-(0001)GaN/RuN superlattice using the Full-Potential Linearized Augmented Plane Waves within Density Functional Theory. We have found that the su-perlattice has a metallic behavior, thus this material is useful as possible contact to GaN. A possible semiconductor-metal-semiconductor or semiconductor-metal device can be designed with this geometry. Reportamos un estudio de las propiedades estructurales y ectrónicas de la superred de período corto 1x1-(0001)GaN/RuN en la fase wurtzita usando FP-LAPW (Full-Potential Linearized Augmented Plane Waves) con DFT (Density Functional Theory). Hemos encontrado que la superred tiene un comportamiento metálico, así este material podría ser útil como un posible contacto para el GaN. Un posible dispositivo semiconductor-metal-semiconductor o semiconductor-metal podría ser diseñado con esta geometría

Research paper thumbnail of Estructura Electronica y Propiedades Estructurales del Compuesto

Información del artículo Estructura Electronica y Propiedades Estructurales del Compuesto Ga0.5V0... more Información del artículo Estructura Electronica y Propiedades Estructurales del Compuesto Ga0.5V0.5N.

Research paper thumbnail of In-composition effect on band gap width of Sc1−xInxN alloys

Journal of Alloys and Compounds, 2009

We report first-principles calculations to analyze the In-composition effect on band gap width of... more We report first-principles calculations to analyze the In-composition effect on band gap width of Sc 1−x In x N alloys in wurtzite structure for the compositions x = 0, 0.25, 0.5, 0.75, 1. The calculations were performed in the framework of the density functional theory (DFT) using the full potentiallinearized augmented plane-wave (FP-LAPW) method as implemented in the WIEN2k code. We used both Perdew-Burke-Ernzerhof (PBE) and Engel-Vosko (EV) functional of generalized gradient approximation (GGA) for the exchange-correlation potential. First, the lattice parameters with PBE functional were optimized. Subsequently, using PBE and EV functional, the band structure at equilibrium volume for each In-concentration was calculated. The gap bowing in wurtzite structure was obtained and analyzed. The calculated band structure with PBE and EV functional for all the compounds are similar, however a band gap wider with EV functional was obtained.

Research paper thumbnail of Estudios AB-INITIO de las propiedades estructurales y electrónicas del nitruro de vanadio

Ciencia e Ingeniería Neogranadina, 2007

En este estudio se presentan las propiedades estructurales y electrónicas del compueston nitruro ... more En este estudio se presentan las propiedades estructurales y electrónicas del compueston nitruro de vanadio VN en las estructuras cloruro de sodio (NaCl), cloruro de cesio (CsCl), blenda de zinc (ZnBl) y wurzita usando cálculos de primeros principios o ab-initio. Se encontró que la fase NaCl es la estructura de cristalización más estable para este compuesto, con parámetro de red a=4.12 A y módulo de volumen Bo= 305 GPa. Los cálculos se realizaron en el marco de la Teoría del Funcional Densidad (DFT), usando el método de Ondas Planas Aumentadas y Linealizadas (FP-LAPW). Los efectos de intercambio y correlación se trataron dentro de la Aproximación del Gradiente Generalizado (GGA), implementada en el método Perdew-Burke-Ernzerhof (PBE).

Research paper thumbnail of Pressure effect on electronic properties of Sc 0.5 In 0.5 N compound

physica status solidi (b), 2009

Research paper thumbnail of Pressure effects on the electronic and magnetic properties of GaxV1−xN compounds: Ab-initio study

Materials Science and Engineering: B, 2009

We report an ab-initio study of the pressure effects on the electronic and the magnetic propertie... more We report an ab-initio study of the pressure effects on the electronic and the magnetic properties of Ga x V 1−x N compounds (x = 0.25, 0.50 and 0.75) in wurtzite-derived structures. We use the full-potential linearized augmented plane wave plus local orbitals method (LAPW + lo) within of the spin density functional theory framework. The lattice constant is found to vary linearly with Ga-concentration. The magnetic moment changes for a critical pressure. At x = 0.75, a rather abrupt onset of the magnetic moment from 0 to 2 B at P cr ∼22.8 GPa is observed. For x = 0.25 and 0.50 Ga concentrations, the magnetic moment increases gradually when the pressure decreases toward the equilibrium value. We study the transition pressure dependence to a ferromagnetic phase near the onset of magnetic moment for each Ga x V 1−x N compounds. The calculation of the density of states with Ga concentration is carried out considering two spin polarizations. The results reveal that for x = 0.75 the compound behaves as a conductor for the spin-up polarization and that the density of states for spin-down polarization is zero at the Fermi level. At this concentration the compound presents a half metallic behavior; therefore this material could be potentially useful as spin injector. At high pressures P > P cr the compounds exhibit a metallic behavior.

Research paper thumbnail of Electronic structure and magnetism in : An ab initio study

Journal of Magnetism and Magnetic Materials, 2009

We carry out first principles spin polarized calculations in order to study the electronic struct... more We carry out first principles spin polarized calculations in order to study the electronic structure and magnetism of Ni 0:0625 Zn 0:9375 O compound using density functional theory (DFT) within a plane-wave ultrasoft pseudopotential scheme. The electronic properties of Ni x Zn 1Àx O at a concentration of 6.25% are analyzed using a 2 Â 2 Â 2 wurtzite ZnO supercell. We optimize the lattice constants of ZnO pure and Ni 0:0625 Zn 0:9375 O. We observe that if one Zn atom is substituted by one Ni atom in the wurtzite ZnO supercell, the lattice parameters decrease slightly some thousandths of angstrom. We also find a stable ferromagnetic state in Ni doped ZnO with a total magnetization of 2:04 m B per supercell. Using the optimized lattice parameters, we have calculated the band structure and density of states of Ni 0:0625 Zn 0:9375 O.

Research paper thumbnail of Barrera de Difusión de un Adsorbato Atómico Sobre la Superficie Bn (0001)-2x2 en Estructura Wurzita

ABSTRACT We have carried out total energy calculations to study the Boron or Nitrogen adsorption ... more ABSTRACT We have carried out total energy calculations to study the Boron or Nitrogen adsorption on w-BN(0001)-2x2 surface. In the calculations, the Konh-Sham equations are solved with the plane wave basis and atomic pseudopotentials using General-ized Gradient Approximation (GGA) for the exchange-correlations potential. We consider the T1, T4 y H3 especial points in order to obtain the more stable reconstruction. We predict that B-T4 y N-H3 structures are the most energetically favorable for rich Boron and Nitrogen configurations, respectively. We find that the atomic adsorption on top of a Boron atom in the surface (site T1) is completely unfavorable. For the Nitrogen adatom we obtained a diffusion barrier of 1,083 eV, while for the Boron adatom was 2.09 eV. Hemos realizado cálculos de energía total para estudiar la adsorción de un átomo de Boro o Nitrógeno sobre la superficie (0001) del w-BN en una geometría 2x2. En los cálculos, se resuelven las ecuaciones de Konh-Sham con una base de ondas planas y pseudopotenciales atómicos, y usando la aproximación de gradiente generali-zado para describir los efectos de intercambio y correlación. Para obtener la reconstrucción más estable consi-deramos los puntos especiales T1, T4 y H3. Predecimos que las estructuras B-T4 y N-H3 son las más favorables energéticamente para configuraciones ricas en Boro y Nitrógeno, respectivamente. Encontramos que la adsor-ción atómica sobre un átomo de Boro de la superficie (sitio T1) es completamente desfavorable. Para el adsor-bato Nitrógeno obtuvimos una barrera de difusión de 1.083 eV, mientras que para el Boro la energía de barrera es de 2.09 eV.

Research paper thumbnail of Estudio de la Superred 1x1-(0001) GaN/RuN, Usando el Método Ondas Planas Aumentadas y Linealizadas con la Teoría del Funcional de la Densidad

ABSTRACT We report a study of the structural and electronic properties of short-period wurtzite 1... more ABSTRACT We report a study of the structural and electronic properties of short-period wurtzite 1x1-(0001)GaN/RuN superlattice using the Full-Potential Linearized Augmented Plane Waves within Density Functional Theory. We have found that the su-perlattice has a metallic behavior, thus this material is useful as possible contact to GaN. A possible semiconductor-metal-semiconductor or semiconductor-metal device can be designed with this geometry. Reportamos un estudio de las propiedades estructurales y ectrónicas de la superred de período corto 1x1-(0001)GaN/RuN en la fase wurtzita usando FP-LAPW (Full-Potential Linearized Augmented Plane Waves) con DFT (Density Functional Theory). Hemos encontrado que la superred tiene un comportamiento metálico, así este material podría ser útil como un posible contacto para el GaN. Un posible dispositivo semiconductor-metal-semiconductor o semiconductor-metal podría ser diseñado con esta geometría

Research paper thumbnail of Estructura Electronica y Propiedades Estructurales del Compuesto

Información del artículo Estructura Electronica y Propiedades Estructurales del Compuesto Ga0.5V0... more Información del artículo Estructura Electronica y Propiedades Estructurales del Compuesto Ga0.5V0.5N.

Research paper thumbnail of In-composition effect on band gap width of Sc1−xInxN alloys

Journal of Alloys and Compounds, 2009

We report first-principles calculations to analyze the In-composition effect on band gap width of... more We report first-principles calculations to analyze the In-composition effect on band gap width of Sc 1−x In x N alloys in wurtzite structure for the compositions x = 0, 0.25, 0.5, 0.75, 1. The calculations were performed in the framework of the density functional theory (DFT) using the full potentiallinearized augmented plane-wave (FP-LAPW) method as implemented in the WIEN2k code. We used both Perdew-Burke-Ernzerhof (PBE) and Engel-Vosko (EV) functional of generalized gradient approximation (GGA) for the exchange-correlation potential. First, the lattice parameters with PBE functional were optimized. Subsequently, using PBE and EV functional, the band structure at equilibrium volume for each In-concentration was calculated. The gap bowing in wurtzite structure was obtained and analyzed. The calculated band structure with PBE and EV functional for all the compounds are similar, however a band gap wider with EV functional was obtained.