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We report on structural properties, elastic constants, mechanical and dynamical stabilities, electronic band structure, and hydrogen storage applications of Mg2FeH6 at zero and high-pressure effects. The work has been realized within the full-potential linearized augmented plane wave method. At zero pressure, the material under study is stable and has a ductile nature. The electronic structure of the material of interest is determined to be X-X wide direct band gap semiconductor with an energy of 1.88 eV. The hydrogen storage capacity wt (%) and the hydrogen desorption temperature are reported as 5.473 and 625.47 K respectively. The Debye temperature ϴD is recorded as 698 K using the elastic constants and about 775 K using the Gibbs calculations. Under high-pressure effect up to 80 GPa, the semiconductor still be an X-X semiconductor with an energy gap of 3.91 eV. The Debye temperature ϴD increases monotonically up to about 1120 K at 80 GPa when using the calculated elastic constants whereas the desorption temperature decreases from 650 to 0 K by increasing pressure from 0 to about 87 GPa. [ABSTRACT FROM AUTHOR]

First-principles all electrons density-functional calculations for the band structure and magnetization of Zn1−xCoxO ternary magnetic alloys, in three phases namely zinc-blende, rocksalt and wurtzite have been reported. The computations are spin-polarized. An inspection of our electronic properties showed that the alloy system of interest exhibits a semiconducting character where the nature of the gap depends on the considered phase. An analysis of electronic charge density suggests that the bonding has a partially covalent character for ZnO which becomes weaker as far as the Co concentration increases. CoO is found to reach a total magnetization of 3 μB per cell for zinc-blende and rocksalt phases and 6 μB per cell for wurtzite phase. [ABSTRACT FROM AUTHOR]

We present a theoretical study on electronic structure and chemical trends of zinc-blende GaP under compression up to 100 kbar obtained from a pseudopotential approach calculations. The influence of high pressure on the features of interest has been examined and reported. The dynamics of chemical bonds in the compound in question is investigated by analyzing the profiles of the electron charge densities. Our findings show generally a good accord with experiment. The present study can contribute in the understanding of the pressure effects on the electronic properties and chemical bonding of GaP material. [ABSTRACT FROM AUTHOR]

Full potential linearized augmented plane wave calculations for the entire range of alloy concentrations of cubic Hg 1-x Mn x Te are reported. The electronic exchange-correlation potential has been treated using the generalized gradient approximation (GGA). For high accuracy of band-gap energies, we used also the modified Becke-Johnson exchange potential with the GGA. Our results are generally in reasonably good accord with data available from the literature. It is found that the lattice parameter of the material system of interest violates Vegard's law. By alloying HgTe with various concentrations of Mn transition metal, Hg 1-x Mn x Te becomes less compressible and the total magnetic moment becomes more important. The analyses of the electronic structure and density of states showed that the alloy system in question exhibits a semiconducting character. The chemical trends of the material under investigation are examined and discussed from an aspect of electronic charge densities. The information obtained in the present study could become good guidance for use of this alloy system in various device applications, e.g., in photoconductive detector applications. • The lattice parameter of Hg 1-x Mn x Te violates Vegard's law. • Hg 1-x Mn x Te exhibits a semiconducting character. • The total magnetic moment becomes very important when increasing the Mn concentration x in Hg 1-x Mn x Te. • The study could become good guidance for use of this alloy system in various device applications. [ABSTRACT FROM AUTHOR]

The composition dependence of direct and indirect band gap energies, anti-symmetric gap, valence band width, refractive index and high-frequency and static dielectric constants has been investigated for GaAs 1-x N x ternary semiconductor alloys with the zinc-blende crystal structure over the whole nitrogen concentration range (x from 0 to 1). The calculations are mainly based on the pseudopotential approach within the virtual crystal approximation. The variation of band-gaps versus nitrogen content show important bowing parameters. Trends in ionicity have been discussed in terms of the anti-symmetric gap. The alloy concentration dependence of the optical parameters of interest is found to be highly nonlinear. [ABSTRACT FROM AUTHOR]

Ab initio calculations based on density functional theory have been performed using the full-potential augmented-plane-wave method so as to investigate the composition dependence of the electronic structure and fundamental properties of hypothetical zinc-blende Cd1-xCoxTe magnetic semiconductor alloys at low Co concentrations. To treat the exchange and correlation energies, the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof has been used. In addition, the modified Becke-Johnson exchange potential with the GGA approach is used for the band structure providing high accuracy. It is found that the addition of a small amount of Co atoms in the Cd1-xCoxTe makes the latter less compressible, ferromagnetic and exhibiting a half metallic character. Besides, the composition dependence of the real and imaginary parts of the dielectric function has been examined and discussed. The information derived from the present study may be useful for spintronics technological applications. [ABSTRACT FROM AUTHOR]

The optical response functions and their derived reflectivity spectrum, the absorption coefficient and the optical conductivity are calculated for zinc-blende-structured Cd1-xMnxTe with Mn concentration in the range 0-1. The evolution of the optical spectra with increased Mn concentrations is examined and discussed. The calculations are performed within the generalized gradient approximation of Engel-Vosko to the density functional theory, and the one-electron equations are solved by means of the full potential linearized augmented plane wave method. Generally, our results are found to be in reasonable agreement with the available experimental and theoretical data reported in the literature. [ABSTRACT FROM AUTHOR]

The results of pseudopotential calculations of the band structure and related electronic and optical properties of quasi-binary (GaP)(ZnSe) crystals in the zinc blende structure are presented. Trends in bonding and ionicity are discussed in terms of electronic charge densities. Moreover, the composition dependence of the refractive index and dielectric constants are reported. The computed values are in reasonable agreement with experimental data. The results suggest that for a proper choice of the composition x, (GaP)(ZnSe) could provide more diverse opportunities to achieve the desired electronic and optical properties of the crystals which would improve the performances of devices fabricated on them. [ABSTRACT FROM AUTHOR]

Abstract: Theoretical investigations of the electronic, optical and elastic properties of cadmium and zinc chalcogenides in the zinc-blende structure are performed using a pseudopotential formalism. Our results are in reasonable agreement with the available experimental data. Polynomial expressions are obtained for the electron effective mass and the static dielectric constant as a function of the fundamental energy band-gap. Relations of elastic constants ratio to the ionicity are also examined and discussed. [Copyright &y& Elsevier]

Abstract: ZnSe and ZnS are the prototype II–VI semiconductors and their cubic phase, which occurs naturally as a mineral, has been called the zinc-blende structure. ZnSe has received particular attention as a blue-lasing material and tremendous experimental efforts have been made to fabricate a sustainable ZnSe blue laser. On the other hand, the ternary system is a good candidate for developing optoelectronic devices such as light emitting diodes (LEDs) or semiconductor lasers. It is also used as waveguides and confinement layers in laser diodes (LDs). In the present study, we have computed the electronic and optical properties of ZnSe, ZnS and using the local model pseudopotential method under the VCA. A central aim of this study is to present the electronic and optical properties of the materials of interest in the zinc-blende structure. [Copyright &y& Elsevier]

Abstract: Information on the energy band gaps, the lattice parameters and the lattice matching to available substrates is a prerequisite for many practical applications. A pseudopotential formalism within the virtual crystal approximation is used to the zinc-blende Al x Ga y In1−x−y N quaternary alloys lattice matched to GaN substrate to predict their energy band gaps and optical properties. The range of compositions for which the alloy is lattice-matched to GaN is determined. Very good agreement is obtained between the calculated values and the available experimental data. The compositional dependence of direct and indirect band gaps and dielectric constants has been investigated. The information derived from this study may be useful for ultraviolet optoelectronic applications. [Copyright &y& Elsevier]

Abstract: The band structure and optical properties of the CdSe x Te1−x ternary mixed crystals have been studied using the pseudopotential formalism under an improved virtual crystal approximation approach. Quantities such as, energy gaps, band-gap bowing parameters, electron effective mass and dielectric constants are calculated. Our results agree well with the available data in the literature. The composition dependence of all studied quantities has been expressed by quadratic polynomial forms. [Copyright &y& Elsevier]

Abstract: Electronic properties and elastic constants of AlN in the wurtzite, zinc-blende and rocksalt structures are investigated using an ab initio pseudopotential method based on the density-functional theory with both the local-density approximation and the generalized gradient approximation for the exchange-correlation functional. The numerically calculated results compare well with the existing experimental data. For elastic constants of rocksalt AlN our results are predictions. [Copyright &y& Elsevier]

Abstract: A pseudopotential formalism within the virtual crystal approximation in which the effects of composition disorder are involved is applied to the Ga x In1−x As y P1−y quaternary alloys in conditions of lattice matching to GaAs, InP and ZnSe substrates so as to predict their energy band gaps. Very good agreement is obtained between the calculated values and the available experimental data for the alloy lattice matched to InP and GaAs. The alloy is found to be a direct-gap semiconductor for all compositions whatever the lattice matching to the substrates of interest. The band-gap ranges and the ionicity character are found to depend considerably on the particular lattice-matched substrates suggesting therefore that, for an appropriate choice of and the substrate, Ga x In1−x As y P1−y could provide more diverse opportunities to obtain desired band gaps, which opens up the possibility of discovering new electronic devices with special features and properties. [Copyright &y& Elsevier]

Based on a pseudopotential scheme, the composition dependence of energy band-gaps of zinc-blende Mg[sub x]Zn[sub 1-x]Se ternary alloys in the composition range of 0≤x≤1 are determined. The effect of deviation of lattice constants of the alloys of interest from Vegard's law on the optical bowing parameter and system transition between the direct and indirect structures is discussed. [ABSTRACT FROM AUTHOR]

• Phase transition pressure from zinc-blende phase to NaCl phase for ZnS and ZnSe. • Phonons and dynamical stability in ZnS and ZnSe at high pressures. • Thermodynamic properties of ZnS and ZnSe in both zinc-blende and rocksalt phases. A pseudopotential study of structural, electronic, elastic and thermodynamic properties of mono-chalcogenides ZnS and ZnSe has been reported. Two phases such as zinc-blende and rocksalt are considered here. The computations are essentially based on the density functional theory within the local density approximation. Physical quantities such as elastic constants and phonon dispersions have been presented. The lattice constants, bulk modulus, entropy and heat capacity and their temperature dependence are analyzed and discussed. Furthermore, the effect of high pressure on the features under investigation of the materials in question is examined. [ABSTRACT FROM AUTHOR]

Abstract Band parameters and superconductivity of yttrium hypocarbide (Y 2 C) have been investigated. The computations are performed using first-principles pseudopotential method within a generalized gradient approximation. The equilibrium lattice parameters have been determined and compared with experiment. Moreover, the material of interest is found to be stiffer for strains along the a-axis than those along the c-axis. A band-structure analysis of Y 2 C implied that the latter has a metallic character. The examination of Eliashberg Spectral Function indicates that Y-related phonon modes as well as C-related phonon modes are considerably involved in the progress of scattering of electrons. By integrating this function, the value of the average electron-phonon coupling parameter (λ) is found to be 0.362 suggesting thus that Y 2 C is a weak coupling Bardeen-Copper-Schrieffer superconductor. The use of a reasonable value for the effective Coulomb repulsion parameter (μ* = 0.10) yielded a superconducting critical temperature T c of 0.59 K which is comparable with a previous theoretical value of 0.33 K. Upon compression (at pressure of 10 GPa) λ and T c are increased to be 0.366 and 0.89 K, respectively, showing thus the pressure effect on the superconductivity in Y 2 C. The spin-polarization calculations showed that the difference in the total energy between the magnetic and non-magnetic Y 2 C is weak. [ABSTRACT FROM AUTHOR]

Structural, electronic, electron-phonon coupling and superconducting properties of the intermetallic compound LuC 2 are investigated by means of ab initio pseudopotential plane wave method within the generalized gradient approximation. The calculated equilibrium lattice parameters yielded a very good accord with experiment. There is no imaginary phonon frequency in the whole Brillouin zone supporting thus the dynamical stability in the material of interest. The average electron-phonon coupling parameter is found to be 0.59 indicating thus a weak-coupling BCS superconductor. Using a reasonable value of μ* = 0.12 for the effective Coulomb repulsion parameter, the superconducting critical temperature T c is found to be 3.324 which is in excellent agreement with the experimental value of 3.33 K. The effect of the spin-orbit coupling on the superconducting properties of the material of interest has been examined and found to be weak. [ABSTRACT FROM AUTHOR]

The dependence on hydrostatic pressure of the electronic and optical properties of zinc-blende AlSb semiconducting material in the pressure range of 0–20 kbar has been reported using a pseudopotential approach. At zero pressure, our findings showed that the electron and heavy hole effective masses are 0.11 and 0.38 m 0 , respectively. Moreover, our results yielded values of 3.3289 and 11.08 for refractive index and high frequency dielectric constant, respectively. These results are found to be in good accord with experiment. Upon compression, all physical parameters of interest showed a monotonic behavior. The pressure-induced energy shifts for the optical transition related to band-gaps indicated that AlSb remains an indirect (Г-X) band-gap semiconductor at pressures from 0 to 20 kbar. The trend in all features of interest versus pressure has been presented and discussed. It is found that the lattice parameter is reduced from 0.61355 to 0.60705 nm when pressure is raised from 0 to 20 kbar. The present investigation may be useful for mid-infrared lasers applications, detectors and communication devices. [ABSTRACT FROM AUTHOR]

A theoretical study is carried out on the fundamental properties of zinc-blende Cd x Zn 1− x Te ternary system using first-principles pseudopotential plane-wave method based on the density functional perturbation theory under the virtual crystal approximation. Electronic exchange and correlation energies are calculated within the local density approximation using the Perdew and Zunger functional parameterization. Features such as lattice constant, elastic constants, sound velocity, Debye temperature, dielectric constants and phonon frequencies have been calculated and their compositional dependence on the Cd content in Cd x Zn 1− x Te has been examined and discussed. Generally, our results are found to be in good agreement with those reported in the literature. The information derived from the present study may be useful for solar cells applications. [ABSTRACT FROM AUTHOR]

Abstract: 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 14eV have also been reported and discussed. [Copyright &y& Elsevier]

Abstract: Li2PtH6 and Na2PtH6 are good candidate for hydrogen storage. The structural, elastic, electronic and optical properties of Li2PtH6 and Na2PtH6 compounds have been investigated using pseudo-potential plane–wave method based on the density functional theory. Computed lattice constant and H atom positional parameter at equilibrium agree well with the available experimental data. A quadratic pressure dependence of the elastic stiffness is found. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young''s modulus, Poisson''s ratio, average sound velocity and Debye temperature are numerically estimated in the framework of the Voigt–Reuss–Hill approximation for Li2PtH6 and Na2PtH6 polycrystalline aggregate. The analyses of the band structure indicates that Li2PtH6 and Na2PtH6 are indirect gap semiconductors. The static dielectric constant and static refractive index are inversely proportional to the fundamental gap. [Copyright &y& Elsevier]

Abstract: The structural, elastic, electronic, optical and thermal properties of α phase in LiBeN semiconductor have been studied using pseudo-potential plane wave method based on the density functional theory. The computed lattice parameter agrees well with previous theoretical work. The elastic constants and their pressure dependence are predicted using the static finite strain technique. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature are numerically estimated in the frame work of the Voigt–Reuss–Hill approximation for α-LiBeN polycrystalline aggregate. The assignments of the structures in the optical spectra and band structure transitions have been examined and discussed. The thermal effect on heat capacities is investigated by the quasi-harmonic Debye model. To the best of our knowledge, most of the studied properties of the material of interest are reported for the first time. [Copyright &y& Elsevier]

Abstract: We present a theoretical study of the electronic structure and optical properties of zinc-blende GaSb1− x N x semiconducting dilute alloys for small amounts of N (0⩽x⩽0.05). Our calculations are based on the pseudo-potential scheme within the virtual crystal approximation that takes into consideration the effects of compositional disorder. In agreement with previous studies, it is found that the introduction of only a few percent of N into GaSb reduces substantially the energy band gaps. It is shown that GaSb1− x N x can be a direct or an indirect semiconductor depending on the N content. Negative band gaps in the material of interest are predicted to occur when the N concentration exceeds 0.026. The information derived from the present study shows that GaSb1− x N x (0⩽x⩽0.017) should enable access to wavelengths in the 2–4μm range. [Copyright &y& Elsevier]

We report on theoretical study of the energy band gaps for the quaternary alloys Zn1−xMgxSySe1−y in conditions of lattice matching to GaAs substrates using simply the empirical pseudopotential method under the virtual crystal approximation which takes into account the effects of compositional disorder. Our results agree generally very well with the available experimental data. It is shown that the band-gap energies of Zn1−xMgxSySe1−y are expressed by the parabolic function of the composition considering the bowing parameter and that Zn1−xMgxSySe1−y can be a direct or an indirect semiconductor depending on the alloy composition. The Zn0.35Mg0.65S0.6Se0.4 is predicted to meet requirement of the cladding layer for fabricating blue double heterostructure laser diodes using ZnS0.06Se0.94 as the active layer. [Copyright &y& Elsevier]

The results of fundamental properties of zinc-blende ZnSe 1− x O x ternary system and related binaries (i.e. ZnSe and ZnO) are reported using the ab initio pseudopotential-density-functional calculations. Features such as lattice constant, bulk modulus, energy gaps and electron effective mass have been determined and their variation as a function of oxygen concentration has been presented and discussed. A good agreement is obtained between the calculated results and existing experimental data. It is found that the lattice constant of the material of interest violates the Vegard's law. The information gathered from the present study could be useful for solar cells technological applications. [ABSTRACT FROM AUTHOR]

Abstract: The investigation of optoelectronic properties of zinc-blende InP x Sb1−x , semiconducting alloys by pseudopotential calculations is studied. The scheme uses the local empirical pseudopotential method, which involves the disorder effect into the virtual crystal approximation by introducing an effective potential disorder. Various quantities for the alloy of interest are calculated. The obtained results show a reasonable agreement with the available experimental data. Special attention has also been given to the compositional dependence of these studied quantities. [Copyright &y& Elsevier]

Abstract: Energy band gaps and electron effective mass as well as their composition dependence are the most critical parameters for band structure calculations of semiconductor alloys. Therefore, an accurate knowledge of these parameters is very important. Unfortunately, there is a limited experimental and theoretical information in the literature regarding the electronic band parameters for zinc blende ZnS x Se1−x . This has incited us to carry out such calculations. For this purpose, we have used the empirical pseudo potential method within the Virtual Crystal Approximation and the effect of compositional disorder is treated as an effective potential. The band gap variation versus sulfur concentration x shows two different behaviors: clear diminution of gap energy for low concentrations, and quasi-linear behavior with a small bowing for large values of x. Furthermore, the calculated effective mass shows that the disorder is not only compositional but also structural. [Copyright &y& Elsevier]