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Perovskite-like materials which include magnetic elements have relevance due to the technological perspectives in the spintronics industry. In this work, the magnetic, structural and electronic properties of the Ba2CoMoO6 double perovskite are investigated. Calculations are carried out through the Full-Potential Linear Augmented Plane Wave method within the framework of the Density Functional Theory with exchange and correlation effects in the Generalized Gradient and Local Density approximations, including spin polarization. From the minimization of energy as a function of volume using Murnaghan's state equation the equilibrium lattice parameter and cohesive properties of this compound were obtained. The study of the electronic structure was based in the analysis of the electronic density of states, and the band structure, showing that this compound evidences a conductive character for a spin channel and insulation for the other, and presents an integer value for the effective magnetic moment (3.0 µB), which allows it to be classified as a half-metallic material. The effects of pressure and temperature on thermophysical properties such as specific heat, Debye temperature, coefficient of thermal expansion and the Grüneisen parameter were calculated and analyzed from the state equation of the system. Obtained results reveal that, in the low-temperature regime, the specific heat at constant volume and pressure presents an analogous behavior to each other, with a tendency to the limit of Dulong-Petit typical of the structures of cubic perovskite-type, showing a value of 246.3 J/mol.K at constant volume and slightly higher values at constant pressure. The dependence of the thermal expansion coefficient, the temperature of Debye and the Grüneisen parameter with the increase in temperature are discussed in relation to other perovskite-like materials. [ABSTRACT FROM AUTHOR]

Copyright of Revista de la Academia Colombiana de Ciencias Exactas, Físicas y Naturales is the property of Academia Colombiana de Ciencias Exactas, Fisicas y Naturales and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Revista de la Academia Colombiana de Ciencias Exactas, Físicas y Naturales is the property of Academia Colombiana de Ciencias Exactas, Fisicas y Naturales and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Perovskite-like materials, which include magnetic elements, have relevance because their technological perspectives of applications in the spintronics industry. In this work, the magnetic, structural, electronic and thermodynamic properties of the Ba2TiMnO6 of the perovskite-like manganite are investigated. Calculations are carried out through the Full-Potential Linear Augmented Plane Wave method (FP-LAPW) within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient (GGA) and Local Density (LDA) approximations, including spin polarization. From the minimization of energy as a function of volume using the Murnaghan's state equation the equilibrium lattice parameter and cohesive properties of this compound were obtained. The study of the electronic structure was based in the analysis of the electronic density of states (DOS), and the band structure, showing that this compound evidences an effective magneticmoment of 3.0 µB. The pressure and temperature dependence of specific heat, entropy, thermal expansion coefficient, Debye temperature and Grüneisen parameter were calculated by DFT from the state equation using the quasi-harmonic model of Debye. A specific heat behavior CV≈CP was found at temperatures below T = 400 K, with Dulong-Petit limit values, which are quite higher than those, reported for simple perovskites. [ABSTRACT FROM AUTHOR]

Se presenta la capacidad de las técnicas de modelización molecular basadas en métodos de la química cuántica para predecir la estructura molecular y electrónica de polímeros conductores. Concretamente, se discute la aplicabilidad de estas herramientas computacionales al estudio de diferentes aspectos del politiofeno y sus derivados: geometría molecular y planaridad, cambios estructurales producidos por el dopado, propiedades electrónicas y desarrollo de nuevos materiales conductores.The ability of molecular modeling techniques based on quantum chemical methods to predict the molecular and electronic structure of organic conducting polymers is examined. More specifically, we report on the applicability of these computational tools to study different aspects of polythiophene and its derivatives: molecular geometry and planarity, the structural changes induced by the doping process, the electronic properties and the design of new conducting materials.

Empleando un esquema de cálculo tight-binding que usa una base de orbitales sp3s*d5, se estudian propiedades de la estructura electrónica de un grupo de materiales semiconductores III-V los cuales son de notable interés para la tecnología de dispositivos electrónicos y optoelectrónicos. En específico, se analiza la influencia sobre estas propiedades de una tensión aplicada según la dirección cristalográfica [111], haciendo uso de una formulación basada en la teoría de la elasticidad para establecer las posiciones relativas de los iones vecinos más próximos. Especial atención se presta a la inclusión del efecto de deformación interna de la red cristalina. Para cada material de los estudiados presentamos las dependencias de las brechas energéticas asociadas a los puntos Γ, X y L de la zona de Brillouin como funciones de la tensión uniaxial en AlAs, GaAs, InAs y GaP. Asimismo, reportamos expresiones de ajuste para los valores de las masas efectivas de conducción en esos cuatro materiales. La comparación de la variación de la brecha de energía en X para el GaP, calculada con nuestro modelo, y recientes resultados experimentales para la transición indirecta entre la banda de huecos pesados y la banda X de conducción arroja una muy buena concordancia.

Empleando un esquema de cálculo tight-binding que usa una base de orbitales sp3s*d5, se estudian propiedades de la estructura electrónica de un grupo de materiales semiconductores III-V los cuales son de interés para la tecnología de dispositivos electrónicos y optoelectrónicos. En específico, se analiza la influencia sobre estas propiedades de una tensión aplicada según la dirección cristalográfica [111], haciendo uso de una formulación presentada en la primera parte del trabajo [Mora-Ramos 2009]. Especial atención se presta a la inclusión del efecto de deformación interna de la red cristalina. Para cada material de los estudiados presentamos las dependencias de las brechas energéticas asociadas a los puntos Γ, X y L de la zona de Brillouin como funciones de la tensión uniaxial en AlP, InP, AlSb, GaSb, InSb. Asimismo, reportamos expresiones de ajuste para los valores de las principales brechas energéticas en esos cinco materiales. Se detecta una fuerte dependencia no lineal de estas magnitudes, así como de las masas efectivas de conducción, con la tensión.

Copyright of Superficies y Vacío is the property of Sociedad Mexicana de Ciencia y Tecnologia de Superficies y Materiales and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Superficies y Vacío is the property of Sociedad Mexicana de Ciencia y Tecnologia de Superficies y Materiales and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Based on the energies and wavefunctions of quantum dot of several geometries, we located these in the sites of a simple cubical lattice and by means of the Tight-Binding method we calculated the supercrystal electronic structure based on quantum dots. We show how the band structure of these supercrystals depends on the parameter of hopping between quantum dots, which is obtained from our artificial molecule calculations. In addition we present a systematic study of electronic properties of quantum dots arrays depending on the effect of the hopping parameter for three different geometries and finally we predict the band gap values for the semiconducting systems. [ABSTRACT FROM AUTHOR]

The most important electronic properties of perovskite SnTiO3 were studied by ab-initio calculations that use DFT with the Generalized Gradient Aproximation (GGA). Taking Muffin-tin's radius of 2.4, 1.8 and 1.75 Bohr for Sn, Ti y O respectively, and considering a simple cubic structure, we found a lattice parameter which is the minimal for cohesion energy of 7.482 Bohr. Looking at the energy band diagram is seen a energy gap of 1.19 eV. The DOS diagram reveals that the contribution of Sn is negligible an energy while O contributes to occupied states. T i have a majoritary contribution for states above fermi level. [ABSTRACT FROM AUTHOR]

The family of the sulvanite compounds are becoming important as possible candidates as p-type transparent conductors with potential applications in solar cells and electrochromic devices. We have investigated by means of first-principle calculations the electronic properties of these materials. The electronic structure shows that these materials are semiconductors with an indirect bandgap. The calculated bandgaps are 1.02, 1.64 and 1.91 eV for Cu3VS4, Cu3NbS4 and Cu3TaS4, respectively. The character of the valance band maximum is dominated by Cu d-states and the character of the conduction band minimum is due to the TM d-states. This bandgap increment is due to the shift of the conduction band minimum to higher energies when we go down in the column V-B of the periodic table. [ABSTRACT FROM AUTHOR]

In this work we report calculations of the cohesive energy in function of volume, within the density functional theory formalism, in order to find the optimum crystallographic parameter of Boron in its simple cubic phase. We found a cohesive energy Eo =-0.389 Ry, a lattice parameter a =1.880 Å and a bulk modulus Bo=2.290 Mbar. These values are in agreement beside 1% with others reported by first-principles methods. Bands structure diagram confirmed that the simple cubic phase of Boron has a conductor behavior. From the density of states, it was concluded that both s and p orbitals contributed to the metallic character of this phase around Fermi level. [ABSTRACT FROM AUTHOR]

We show the variation on band energy structure, density of states, energy gap and lattice constant of diamond carbon phase when pressure is increased from 0 to 240 GPa. The study was made from first principles using the Density Functional Theory within the generalized gradient approximation. In this interval of pressure variation we found that the bands shape is very stable, the indirect semiconductor characteristic is preserved, and in the valence band p orbital contribution is more important around the Fermi level. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of A2FeMoO6 (A=Ba, Ca), are studied by using ab initio band structure methods. The total and partial densities of states are calculated for each spin polarization on the compounds. As a result, the half metallic property was found on both compounds. Besides, the partial densities of states permitted to infer the mechanism of conduction on this compounds family, based on the Sarma's model. [ABSTRACT FROM AUTHOR]

The electronic states were calculated in volume for the semiconductors Silicon (Si) and Germanium (Ge), using the method Tight-Binding (TB), keeping in mind interactions up to first neighbors. The matrix Hamiltonian was built using a base of orbital atomic s, p and the excited states s*. Based in this approach you proceeded to calculate the relationships of dispersion of the energy E against wave number ᵏ̄, for some addresses of high symmetry in the first zone of Brillouin (PBZ). The characters of the bands and the densities of states were determined (DOS) total and partial according to the orbital characters of the different ones used in the base in which the matrix hamiltonan was written. [ABSTRACT FROM AUTHOR]

Using first principles calculations by means the Full-Potential Linearized Plane Wave (FP-LAPW) method, the structural and electronic properties of Ga0.5V0.5N in NaCl and wurtzite structures have been investigated. For wurtzite structure relation c/a and internal parameter u were optimized, with these values: equilibrium volume, lattice constant, cohesion energy and bulk modulus were determinated. Wurtzite was the calculated ground-state structure with lattice constant a=5.953 bohr and bulk modulus B=191.9 GPa. An additional local minimum in the NaCl structure with total energy 0.350 eV/(formula unit) higher was found. On the other hand, band structure calculations for equilibrium volume of Ga0.5V0.5N were presented. Material exhibits metallic behaviour because it does not have an energy gap. [ABSTRACT FROM AUTHOR]

El SNO2 es un buen candidato para utilizarse como capa transportadora de electrones en la estructura de celdas solares basadas en perovskitas hibridas MAPbX, esto debido a que presenta una excelente compatibilidad de la heterounión debido al acoplamiento de las bandas de conducción y valencia de estos materiales, además la conductividad del SNO2 es de 3x10² S cm-1 y una presenta una tasa de transmisión de vapor del orden de 10-6 g (m² día)-1, estando en el orden de magnitud que se exige en el encapsulado de OLED1. Para el estudio de la modificación de la estructura de bandas, se utilizaron diferentes condiciones de depósito por medio de Atomic Layer Deposition (ALD) y Plasma Enhanced Atomic Layer Deposition (PEALD) variando los agentes oxidantes, utilizando vapor de agua, O3, así como plasmas remoto y directo de agua y O2. En dependencia de la oxidación utilizada, se tienen distintos defectos en el material, los cuales modifican la función de trabajo, band gap, así como las posiciones de la banda de conducción y valencia respecto al nivel de Fermi. Los defectos se deben principalmente a la reactividad de los agentes oxidantes, siendo esta mayor en el uso del PEALD respecto al ALD. Utilizando la técnica de XPS fue posible determinar estos parámetros a través del estudio de los electrones de alta energía cinética para el caso del máximo de la banda de valencia, los de baja energía cinética para la determinación de la función de trabajo y los electrones dispersados inelásticamente en la región de emisión del O1s para el band gap. Así mismo, se determinó que el estado de oxidación Sn4+ se encuentra presente en las películas delgadas obtenidas por todos los métodos de oxidación utilizados, identificándose a través del perfil del espectro de banda de valencia. A partir de esta información es posible identificar en dependencia de la estructura de la celda solar que se desee fabricar, el método adecuado para el depósito del SNO2. [ABSTRACT FROM AUTHOR]