Jairo Arbey Rodríguez

Incorporation of iron on the clean and gallium-bilayer GaN(0001) surface

First-principles calculations of the energetic and magnetic properties of Fe incorporation in various sites on clean and Ga-bilayer GaN(0001) surfaces are presented. Employing a thermodynamic approach, the calculated formation energies demonstrate characteristic features in the structural stability and magnetism of Fe incorporated surfaces depending on the growth condition. It is found that the N-rich conditions produce greater magnetization compared to the Ga-rich condition. N-rich magnetization is attributed to the interface formation of FeN layers on the GaN(0001) surface. In addition, calculations for Fe incorporation in Ga-bilayer terminated surface suggest that it is possible to form a FeGax ferromagnetic alloy by performing the growth under extreme Ga-rich conditions.

Structural and Electronic Properties of ScC and NbC: A First Principles Study

We study the structural and electronic properties of scandium carbide ScC and niobium carbide NbC in both the sodium chloride rock salt (NaCl) and wurtzite structures by means of accurate first principles total energy calculations. The calculations were performed employing the full-potential linearized plane wave method (FP-LAPW). We used the generalized gradient approximation (GGA) of Perdew Burke and Ernzerhof for the exchange and correlation potential. Volume optimization and density of states including spin (DOS) of the systems are presented.

First Principles Study of the Structural, Electronic, and Magnetic Properties of ZrC

Zirconium carbide (ZrC) is technologically important in devices that must function at high temperatures, and its ground state is a NaCl like structure. Changes of the structure and electronic properties of ZrC under high pressure were studied within the framework of density functional theory (DFT). This research was performed for several structures, such as NaCl type (B1), CsCl type (B2), ZnS type (B3), wurtzite type (B4) and NiAs type (B8) structures for ZrC, looking for possible phase transitions induced by high pressure, and four phase transitions were found: the first is the well-known phase transition from the B1 structure to the B2 structure, which occurs at around ~291 GPa. Additionally, in the present paper we found other phase transitions: from the B8 structure to the B2 structure, from the B4 structure to the B2 structure, and lastly from the B3 structure to the B2 structure. Electronic bands are exhibited at zero pressure and temperature (with spin-orbit coupling) for the five structures. For the transition from the B1 structure to the B2 structure, bands are exhibited for two pressures, one before and the other after the transition occurs. The band structure shows that all the structures studied are metallic and nonmagnetic, with the exception the B3 structure, which exhibits a semi-metallic and nonmagnetic behaviour.

Theoretical investigation of GaN carbon doped

In this work we used first principles calculations in the frame of density functional theory (DFT) in order to study the structural and electronic properties of GaN doped with carbon. The computational calculations were carried out by a method based on plane waves pseudopotentials, as implemented in the Quantum Espresso code. In the wurtzite type GaN supercell the nitrogen atoms were replaced by carbon atoms (C by N) and then also the gallium atoms by carbon atoms (C by Ga). The carbon concentrations in the GaN volume was set as x=25, 50 y 75%. For each concentration x of carbon the formation energy was calculated for the substitutions C by N and CxGa. We found that it is more energetically favourable that the carbon atoms occupy the positions of the nitrogen atoms (C by N), because in all the x concentrations of carbon the formation energies were lower than that in the substitutions (C by Ga). It was found that the new compounds CxGaN1-x have higher bulk moduli. So they are very rigid. This property makes them good candidates for applications in hard coatings or devices for high power and temperatures. Analysis of the density of states show that the new CxGaN1-x ternary compound have metallic behaviour that comes essentially from the hybridization states N-p and C-p cross the Fermi level.

Propiedades estructurales, electrónicas y magnéticas de la perovskita BiRO3

Presentamos un estudio detallado de las propiedades estructurales, los estados, electronicos y magneticos de las perovskitas del tipo BiRO3, con R=Fe, Co, Ni, en su estructura cubica, con grupo de simetria Pm-3m. En la obtencion de los resultados se utilizo el metodo de Spin Polarizado de Ondas Planas Aumentadas y Linealizadas (SP-FP-LAPW) dentro del marco de la teoria DFT. El estudio estructural consistio en calcular las energias de cohesion en funcion del volumen y mediante su ajuste a la ecuacion de estado de Murnaghan se determinaron el modulo de volumen, el volumen de equilibrio y de este el valor de constante de red. En el estudio de las caracteristicas electronicas se han determinado curvas de energia en contra del numero de onda (k) y la densidad de estado (DOS) para cada polarizacion de spin.