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Abstract: The structural, elastic, electronic and optical properties of the gallium monohydrides BaGaXH (X=Si, Ge, Sn) have been investigated by means of first principles calculations. The low values of the B/G ratio of these compounds correspond to the brittle nature, which is due to the hydrogen presence. The bulk modulus, Young's modulus, shear modulus decrease from Si to Sn for BaGaXH (X=Si, Ge, Sn) in the same column in the periodic table. Also the Debye temperature of these compounds has a relative high value indicating that they possess good thermal conductivity. The mean sound velocities have a progressive decrease from silicon (Si) to tin (Sn). [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: A computed investigation on the structural, elastic, electronic, phonon frequencies and thermal properties of Al x Sc y B 1−x−y N quaternary alloys in the zinc-blend phase has been made with first-principles methods. The information on the lattice constant, lattice matching to AlN substrate and energy band gaps is indispensable for various practical applications. We have studied the effect of Sc concentration y (y =0, 0.152, 0.303, 0.455 and 0.607) on the lattice constant, bulk modulus, elastic constants C 11, C 12 and C 44, band gaps, optical phonon frequencies (ω TO and ω LO ), static and high-frequency dielectric coefficient ɛ(0) and ɛ(∞) and dynamic effective charge Z*. We remark an important deviation from the linear concentration dependence of the lattice constant and bulk modulus. The shear moduli, Young''s modulus, Poisson''s ratio were estimated in the frame work of the Voigt–Reuss–Hill approximation. The resistance to changes in bond length and lateral expansion in Al x Sc y B 1−x−y N increase with increasing y concentration. We observe that at y concentration about 0.11, the Г–X indirect fundamental gap becomes Г–Γ direct fundamental gap in Al x Sc y B 1−x−y N. There is well agreement between our results and the experiment data for AlN binary compound which is a support for those of the quaternary alloys that we report for the first time. [Copyright &y& Elsevier]

Abstract: A theoretical study on the structural, elastic, electronic and lattice dynamic properties of Al x Y y B1−x−y N quaternary alloys in zinc-blend phase has been carried out with first-principles methods. Information on the lattice parameter, the lattice matching to available substrates and energy band-gaps is a prerequisite for many practical applications. The dependence of the lattice parameter a, bulk modulus B, elastic constants C 11, C 12 and C 44, band-gaps, optical phonon frequencies (ω TO and ω LO ), the static and high-frequency dielectric coefficients ε (0) and ε (∞) and the dynamic effective charge Z ⁎ were analyzed for y=0, 0.121, 0.241, 0.362 and 0.483. A significant deviation of the bulk modulus from linear concentration dependence was observed. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young''s modulus, Poisson''s ratio are numerically estimated in the frame work of the Voigt–Reuss–Hill approximation. The resistance to changes in bond length and lateral expansion in Al x Y y B1−x−y N increase with increasing y concentration. We observe that at y concentration about 0.035 and 0.063, Al x Y y B1−x−y N changes from brittle to ductile and Γ–X indirect fundamental gap becomes Γ–Γ direct fundamental gap. There is good agreement between our results and the available experimental data for the binary compound AlN, which is a support for those of the quaternary alloys that we report for the first time. [Copyright &y& Elsevier]

Abstract: The structural, elastic, electronic, optical and thermal properties of the semiconductor perovskite CsPbCl3 were investigated using the pseudo-potential plane wave (PP-PW) scheme in the frame of generalized gradient approximation (GGA) and local density approximation (LDA). The computed lattice constant agrees reasonably with experimental and theoretical ones. The CsPbCl3 crystal behaves as ductile material. The valence bands are separated from the conduction bands by a direct band gap R–R. We distinguished hybridization between Pb-p states and Cl-p states in the valence bonding region. Under compression at P=30GPa, this material will have a metallic character. The thermal effect on the lattice constant, bulk modulus, Debye temperature and heat capacity C V was predicted using the quasi-harmonic Debye model. To the author''s knowledge, most of the studied properties are reported for the first time. [Copyright &y& Elsevier]

Abstract: The structural, elastic, electronic, optical and thermodynamic properties of the perovskite chloride CsCdCl3 were investigated using the pseudo-potential plane wave (PP-PW) within the Generalized Gradient Approximation (GGA) and Local Density Approximation (LDA). The computed lattice parameter agrees well with experimental and previous theoretical works. Based on the elastic constants and their related parameters, the crystal rigidity and mechanical stability have been discussed. Energy band structure shows that the investigated material is indirect energy band gap semiconductor. The static dielectric constant and static refractive index are indeed, proportional to the fundamental indirect band gap. The thermal effect on the lattice parameter, bulk modulus, volume expansion coefficient, Grüneisen parameter, heat capacities and Debye temperature were predicted using the quasi-harmonic Debye model. To the best of the authors’ knowledge, most of the studied properties are reported for the first time. [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 plane-wave method as implemented in the ABINIT code is used to the As x P y N1−x−y Al quaternary alloys lattice matched to AlP substrate to predict their energy band gaps and optical properties. The range of compositions for which the alloy is lattice-matched to AlP is determined. Very good agreement is obtained between the calculated values and the available experimental data. The Debye temperature increase when the bulk modulus is enhanced. We study the variation of elastic constants, the optical phonon frequencies (ω TO and ω LO ), the static and high-frequency dielectric coefficient ɛ(0) and ɛ(∞) and the dynamic effective charge Z * with P concentration (y). [Copyright &y& Elsevier]

Abstract: The structural, elastic, electronic and optical properties of XO (X= Ca, Sr and Ba) compounds were investigated by the density functional theory. A good agreement was found between our calculated results and the available theoretical and experimental data of the lattice constants. Young''s modulus, Poisson ratio, bulk modulus, elastic constants and their pressure derivatives are also calculated. SrO and BaO compounds present a transition phase at 39.72 and 27.28GPa. The SrO compound shows a change from direct band gap (Γ–Γ) to indirect band gap (Γ–X) at about 15GPa. The top of the valence bands reflects the s electronic character for all structures. We investigate the effective mass of electrons as function of pressure at the Γ point for CaO, SrO and BaO compounds. Calculations of the optical spectra have been performed for the energy range 0–60eV. The origin of the spectral peaks was interpreted based on the electronic structures. The enhancement of pressure increases the static dielectric function and refractive index of CaO, SrO and BaO. [Copyright &y& Elsevier]

Abstract: The stability, structural parameters, elastic constants, electronic and optical properties of perovskites CsCaH3 and RbCaH3 were investigated by the density functional theory. The calculated lattice parameters are in agreement with previous calculation and experimental data. The energy band structures, density of states, born-effective-charge and Mulliken charge population were obtained. The perovskites CsCaH3 and RbCaH3 present a direct band gap of 3.15eV and 3.27eV at equilibrium. The top of the valence bands reflects the s electronic character for both structures. Furthermore, the absorption spectrum, refractive index, extinction coefficient, reflectivity, energy-loss spectrum, and dielectric function were calculated. The origin of the spectral peaks was interpreted based on the electronic structures. The static dielectric constant and refractive index are indeed, inverse proportional to the direct band gap. [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 plane-wave method as implemented in the ABINIT code is used to the As x P y N1− x − y B quaternary alloys lattice matched to BP substrate to predict their energy band gaps and lattice dynamic properties. The range of compositions for which the alloy is lattice matched to BP 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 has been investigated. We study the variation of elastic constants, the optical phonon frequencies (ω TO and ω LO), the high-frequency dielectric coefficient ε(∞) and the born effective charge Z ∗ with P concentration. [Copyright &y& Elsevier]

Abstract: We present structural, elastic, electronic and optical properties of the perovskites SrMO3 (M=Ti, and Sn) for different pressure. The computational method is based on the pseudo-potential plane wave method (PP-PW). The exchange-correlation energy is described in the generalized gradient approximation (GGA). The calculated equilibrium lattice parameters are in reasonable agreement with the available experimental data. This work shows that the perovskites SrTiO3, and SrSnO3 are mechanically stable and present an indirect band gaps at the Fermi level. Applied pressure does not change the shape of the total valence electronic charge density and most of the electronic charge density is shifted toward O atom. Furthermore, in order to understand the optical properties of SrMO3, the dielectric function, absorption coefficient, optical reflectivity, refractive index, extinction coefficient and electron energy-loss are calculated for radiation up to 80 eV. The enhancement of pressure decreases the dielectric function and refractive indices of SrTiO3 and SrSnO3. [Copyright &y& Elsevier]

Abstract: The alkaline platinum hydrides are considered the most promising as hydrogen storage materials. The alloying ability of crystal, elastic constants and related parameters, electronic and optical properties have been studied using pseudo-potential plane–wave method based on the density functional theory. The investigated compounds show a weaker resistance to compression along the principal a-axis and their resistance to shear deformation is lower than the resistance to the unidirectional compression. The band structure indicates that A2PtH6 (A=K, Rb and Cs) are X–X direct gap semiconductors. The effective electron mass at equilibrium has been predicted towards X–Γ, X–W and L–W directions. The strong hybridization between Pt-d and H-s states in the upper valence band translates the existence of covalent bonding character in these compounds. The static optical dielectric constant is inverse proportional to the fundamental gap. [Copyright &y& Elsevier]

Abstract: Structural, electronic and optical properties of the ZnSc2S4 and CdSc2S4 cubic spinels have been investigated by means of the full-potential (linearized) augmented plane wave plus local orbitals based on density functional theory. The exchange-correlation potential is treated by the GGA–PBEsol [J.P. Perdew, A. Ruzsinszky, G.I. Csonka, O.A. Vydrov, G.E. Scuseria, L.A. Constantin, X. Zhou, K. Burke, Phys. Rev. Lett. 100 (2008) 136406] and the recently proposed modified Becke–Johnson potential approximation (mBJ) [F. Tran, P. Blaha, Phys. Rev. Lett. 102 (2009) 226401], which successfully corrects the band-gap problem found with GGA for a wide range of materials. The obtained structural parameters are in good agreement with the available experimental data. This gives support for the predict properties for ZnSc2S4 and CdSc2S4. The band structures reveal that both compounds are semiconductor with a direct gap. The obtained gap values show that mBJ is superior for estimating band gap energy. We have calculated the electron and hole effective masses in different directions. The density of states has been analyzed. Based on our electronic structure obtained using the mBJ method we have calculated various optical properties, including the complex dielectric function ɛ(ω), complex index of refraction n(ω), reflectivity coefficient R(ω), absorption coefficient α(ω) and electron energy-loss function L(ω) as functions of the photon energy. We find that the values of zero-frequency limit ɛ 1(0) increase with decreasing the energy band gap in agreement with the Penn model. The origin of the peaks and structures in the optical spectra is determined in terms of the calculated energy band structures. [Copyright &y& Elsevier]

• Some Physical properties for BeO 1−x A x alloys are investigated. • The calculated ground states properties for BeA compounds compare well with the available data. • Alloying BeO and BeX change the nature of band gap compared to the parent compounds. • The optical and the thermodynamic properties for are investigated for the first time. Special quasi-random structure (SQS) was used to investigate the structural, electronic, and optical characteristics of the binary and ternary beryllium chalcogenide alloys. The computations were performed using the pseudopotential technique. The GGA-WC scheme was applied to study the structural and optical features of these present alloys, while the HSE06 hybrid functional was used to correct the underestimation of the electronic band structure. The optimized lattice constants and bulk modulus demonstrate a non-linear tendency with increasing x concentration. The phase transition may occur for all ternary alloys at x = 0.5 with the orthorhombic assumed crystal system. The ternary alloys of BeO 1− x A x (A = S, Se) at 0.5 ⩽ x ⩽ 1 have an indirect band gap, while BeO 1− x Te x 0.5 ⩽ x ⩽ 1 manifest a metallic demeanor using HSE06 formalism. The optical spectra were computed and discussed in detail. Furthermore, the thermodynamic stability of the studied compounds was examined using the miscibility critical temperature. [ABSTRACT FROM AUTHOR]