First-principles calculations are performed to study the structural, electronic, thermodynamic and thermal properties of the InP and InAs bulk materials and InAs x P 1-x ternary alloys using the full potential-linearized augmented plane wave method (FP-LAPW) within the density functional theory (DFT). The dependence of the lattice constant, bulk modulus, band gap, Debye temperature, heat capacity and mixing entropy on the composition x was analyzed. The lattice constant for InAs x P 1-x alloys exhibits a marginal deviation from the Vegard's law. A large deviation of the bulk modulus from linear concentration dependence (LCD) was observed for our alloys. We found that the composition dependence of the energy band gap is almost linear by using the mBJ and EV-GGA approximations. The microscopic origins of the gap bowing were explained and detailed by using the approach of Zunger and co-workers. Furthermore, the calculated phase diagram shows a miscibility gap for these alloys with a high critical temperature. Thermal effects on some macroscopic properties of InAs x P 1-x alloys are predicted using the quasi-harmonic Debye model, in which the phononic effects are considered. This is the first quantitative theoretical prediction of the thermal properties of the InAs x P 1-x alloys, and we still expect the confirmation of experimental studies.

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First-principle calculations were performed to study the structural, electronic, thermodynamic and thermal properties of ZnS x Se 1−x ternary alloys using the full potential-linearized augmented plane wave method (FP-LAPW) within the density functional theory (DFT). In this approach the Wu-Cohen generalized gradient approximation (WC-GGA) and Perdew-Wang local density approximation (LDA) were used for the exchangecorrelation potential. For band structure calculations, in addition to WC-GGA approximation, both Engel-Vosko (EV-GGA) generalized gradient approximation and recently proposed modified Becke-Johnson (mBJ) potential approximation have been used. Our investigation on the effect of composition on lattice constant, bulk modulus and band gap for ternary alloys shows a linear dependence on alloy composition with a small deviation. The microscopic origins of the gap bowing were explained using the approach of Zunger and co-workers. Besides, a regular-solution model was used to investigate the thermodynamic stability of the alloys which mainly indicates a phase miscibility gap. Finally, the quasi-harmonic Debye model was applied to see how the thermal properties vary with temperature at different pressures.

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