First principles calculations of structural, electronic and thermodynamic properties of SrS, SrSe, SrTe compounds and SrS1−xSex alloy

The ab initio full potential linearized augmented plane wave (FP-LAPW) method within density functional theory was applied to study the structural and electronic properties of the compounds SrS, SrSe, SrTe and their alloy SrS1−xSex in the NaCl structure. Results are obtained using both the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation potentials. The ground-state properties, like lattice constant and bulk modulus obtained from our calculations agree very well with experimental and other theoretical calculations. We present the main features of electronic properties, where the electronic band structure shows that the fundamental energy gap is indirect . Moreover the alternative form of GGA proposed by Engel and Vosko (GGA-EV) is also used for band structure calculations. Results obtained with this approximation show that significant improvement over other theoretical work are closer to the experimental data. The effect of composition on lattice parameter and bulk modulus was investigated.Deviations of the lattice constant from Vegard’s law and the bulk modulus from linear concentration dependence were observed for the alloy. Moreover, the microscopic origins of the gap bowing were explained. In addition the thermodynamic stability of the alloy was investigated by calculating the critical temperature for SrS1−xSex alloy.