Structural, elastic and electronic properties for M2XC （M--Ti and Cr, X--Ga and A1） phases from ab initio calculations

The first-principles study of the structural, elastic and electronic properties of the M 2 XC phases depending on the type of M transition metal (M are Ti and Cr) and on X (X are Ga and Al) was reported. The calculations are performed using the pseudo-potential plane-wave approach in both the local density and generalized gradient approximations. The elastic constants are calculated using the static finite strain technique. Features such as structural and elastic parameters, Debye temperature, sound velocities and their pressure dependence have been investigated. In agreement with experimental and previous theoretical findings, it is found that the compressibility along a and c axis depends on the valence electron concentration (VEC). Correlations revealing the governing role of the X and M elements on the machinability indices of the material have been examined. The electronic properties have been discussed in terms of chemical bonding showing that bonding is due to Md-Cp and Md-Xp hybridizations. M-C bonds are stiffer than M-X ones and Al-Ti (Cr-C) bonds are stiffer than those corresponding to Ti-C (Al-Cr). It is shown that the stiffness of the M-X and M-C bonds increases with increasing the number of VEC.     

The effect of hydrostatic pressure on the electronic and optical properties of InP

Based on the empirical pseudo-potential method, the electronic and optical properties of the InP compound in the zinc-blende structure at ambient and under hydrostatic pressure are reported. The first-order pressure coefficients of the main band gaps (at Γ, X, and L) are given. The agreement between our calculated hydrostatic deformation potential and the available experimental data is better than 5%, whereas for the crossover pressure from direct to indirect band gap is about 10% less. The valence bandwidth increases with increasing pressure reflecting the decreased ionicity in the material of interest. Besides the electronic properties, the effect of pressure on the dielectric function is also analysed.     

Ab initio study of structural,electronic, phase diagram,and optical properties of CdSe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">1−x</Emphasis></Subscript> semiconducting alloys

Based on the self-consistent ab initio full potential-linearized augmented plane wave method, the structural, electronic, optical, and thermodynamic properties of CdSe _x Te_1−x ternary semiconductor alloys have been investigated. The exchange–correlation potential was calculated using both the generalized gradient approximation (GGA) by Perdew–Burke–Ernzerhof (PBE) and the GGA by Engel–Vosko (EV-GGA). The ground-state properties are determined for the cubic bulk materials CdSe, CdTe, and their mixed crystals at various concentrations (x = 0.25, 0.5, and 0.75). Deviation of the lattice parameter from Vegard’s law and the bulk modulus from linear concentration dependence has been examined. The microscopic origins of the band-gap bowing parameter have been discussed. Moreover, the refractive index and the optical dielectric constant for CdSe _x Te_1−x are studied using different models. Besides, the thermodynamic stability of the alloys of interest is investigated by means of the miscibility critical temperature.     

Investigated optical and elastic properties of Porous silicon: Theoretical study

Compatibility between experimental and theoretical works is achieved. Empirical Pseudopotential Method (EPM) is used to calculate the energy gap of Si which is found to be indirect. Features such as refractive index, optical dielectric constant, bulk modulus, elastic constants and short-range force constants have been investigated. In addition to the shear modulus, Young’s modulus, Poisson’s ratio and Lame’s constants for both bulk Si (p = 0%) and Porous silicon (PS) are derived. The calculated results are found to be in good agreement with other experimental and theoretical ones. Also, the Debye temperature of PS is estimated from the average sound velocity. To our knowledge, the optical properties using specific models and elasticity of PS are reported for the first time.     

First principles study of structural,electronic and optical properties of AgSbS2

In this work, we study the structural, electronic and optical properties of AgSbS₂, using full-potential linearized augmented plane wave and the pseudopotential plane wave scheme in the frame of generalized gradient approximation. Features such as the lattice constant, bulk modulus and its pressure derivative are reported. Our results suggest a phase transition from AF-IIb phase to rocksalt (B1) phase under high pressure. The calculated band structure and density of states show that the material under load has an indirect energy band gap X→(LГ) for AF-IIb phase (semiconductor) and a negative band gap W→(ГX) for B1 phase (semimetal). The optical properties are analyzed and the origin of some peaks in the spectra is discussed. Besides, the dielectric function, refractive index and extinction coefficient for radiation up to 14 eV have also been reported and discussed.     

Electronic properties of GaxIn1−xP from pseudopotential calculations

Based on a pseudopotential scheme within the virtual crystal approximation, we present a theoretical investigation of the electronic properties of Ga_xIn_1−xP. The effect of alloy disorder on energy band-gaps has been examined and found to be not negligible. The composition dependence of energy band-gaps and electron effective mass is shown to be non-linear. In agreement with experiment, a direct-to-indirect band-gap crossover is found to occur close to x = 0.7. Besides, the electron valence and conduction charge densities for Ga_0.50In_0.50P derived from pseudopotential band-structure calculations are reported and trends in bonding and ionicity are discussed.     

Pressure dependence of the electronic structure in germanium

Based on the pseudopotential formalism of Ge, which can describe the electronic energy structure over a wide energy range of more than 20 eV from the bottom of the valence band, calculations of the pressure dependence of the energy gaps and charge densities have been performed. The predictions for the pressure coefficient are consistent with the experiment. The valence charge densities of Ge under high pressure are studied. The forbidden X-ray structure factor F(222) is stable under pressure and varies less than 3% under volume changes as big as 5%.     

Zinc-Blende MnTe Under Pressure: Structural,Mechanical, and Optical Properties from Ab Initio Calculation

We present first-principles studies of structural, mechanical, and optical properties of zinc blende MnTe using the pseudopotential plane-wave method within the local density approximation. The effect of hydrostatic pressure on investigated properties has been examined and discussed. At zero pressure, our results are found to agree reasonably well with those reported in the literature. The generalized elastic stability criteria showed that the material of interest is mechanically stable in all the studied pressure ranges. Applied pressure is found to shift all optical spectra under consideration, giving new optical parameters.     

Structural and Thermo-Physical Properties of 3C-SiC: High-Temperature and High-Pressure Effects

Silicon - Based on the density functional theory (DFT), a systematic theoretical investigation on the structural parameters and finite temperature thermo-physical properties of cubic silicon...     

Optoelectronic and dielectric properties of GaAs x Sb1-x ternary alloys

Based on the pseudopotential scheme under the virtual crystal approximation in which the effect of compositional disorder is involved, the dependence of optoelectronic properties of GaAs _x Sb_1-x on alloy composition x have been studied. Our results showed generally good agreement with the available experimental data. The material of interest is found to exhibit features of both direct and indirect band-gap semiconductor depending on the alloy composition x. The method used has been combined with the Harrison bond-orbital model and employed to calculate the dielectric constants and their composition dependence.