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a b s t r a c tStructural properties, electronic band structure, real and imaginary parts of complex dielectric function of alkali chloride XCl (K, Rb and Li) compounds were investigated under various pressures using first principles calculations. Moreover, Gibbs free energies were also calculated at those pressures. Calculated results of the Gibbs free energy show that LiCl does not show any structural phase transition. However, structural phase transitions of KCl and RbCl occur from NaCl (B1) to CsCl (B2) at 4.5 and 1.7 GPa pressures, respectively. The electronic band gaps under pressure were also calculated. The calculated physical properties of these compounds are compared with the previous theoretical and experimental results and a good agreement was observed.

The electronic energy band structure and linear optical properties of the ferroelectric semiconductor SbSI in the paraelectric phase are calculated by an ab initio pseudopotential method using density functional theory in the local density approximation. The calculated electronic band structure shows that SbSI has an indirect band gap of 1.45 eV and that the smallest direct gap is at the S point of the Brillouin zone (1.56 eV). The total density of states has been analysed. The linear energy dependent dielectric functions and some optical constants such as the absorption coefficient, extinction coefficient, refractive index, energy-loss function, reflectivity and optical conductivity, including self-energy effects, are calculated. The effective number of valence electrons and the effective optical dielectric constant are also calculated.

Abstract:Using the first-principles band-structure method, we have calculated the structural and electronic properties of zincblende TlAs, TlP, GaAs and GaP compounds and their new semiconductor Tl Ga 1− As P 1− quaternary alloys. Structural properties of these semiconductors are obtained with the Perdew and Wang local-density approximation. The lattice constants of Tl Ga 1− As, Tl Ga 1− P ternary and Tl Ga 1− As P 1− quaternary alloys were composed by Vegard's law. Our investigation on the effect of the doping (Thallium and Arsenic) on lattice constants and band gap shows a non-linear dependence for Tl Ga 1− As P 1− quaternary alloys. The band gap of Tl Ga 1− As P 1− , E ( ) concerned by the compositions and . To our awareness, there is no theoretical survey on Tl Ga 1− As P 1− quaternary alloys and needs experimental verification. 71.15.Mb, PACS (2008): Keywords:density functional theory • electronic structure of disordered solids • electron density of states and band structure of crystalline solids © Versita sp. z o.o.

The electronic band structures of some A 5 B 6 C 7-type ternary compounds, BiSeI , BiSI , BiSCl , BiSBr , BiSeBr and SbSeBr , are investigated using the density functional theory and pseudopotential theory under the generalized gradient approximation (GGA). The electronic band structures obtained show that these crystals, except for BiSeI , have an indirect band gap.