First-principles calculations are performed to study the structural, electronic and properties of Zn1-xMgxSeyTe1-y alloys using the full potential-linearized augmented plane wave method (FP-LAPW) within the density functional theory(DFT).In this approach the Perdew-Burke-Ernzerhorf generalized gradient approximation (PBE-GGA) was used for the exchange-correlation potential. Moreover, the modified Becke Johnson approximation (mBJ) was also used for band structure calculations. Firstly we studied the MgX binary compounds. The lattice constant for the ternary alloys exhibits a small deviation from the Vegard's law. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. The bowing of the fundamental gap versus composition predicted by our calculations is in good agreement with available theoretical data. In addition, we have studied the thermal properties of these alloysusing the Debye model implemented in Gibbs program. Finally, the energy band gap of Zn1-xMgxSeyTe1-y quaternary alloys lattice matched to In As and ZnTe substrats was investigated. To our knowledge this is the first quantitative theoretical investigation on Zn1-xMgxSeyTe1-yquaternaryalloys and still awaits experimental confirmations.

Quaternary alloys, Functional density(DFT), Approximation of the generalized gradient (PBE-GGA) ,mBJ approximation, InAs and ZnTe substrates.