AB INITIO CALCULATION OF THE LATTICE DYNAMICS OF THE ZnSe1-xTex ALLOY

The lattice dynamics of the ternary ZnSe1-xTex alloy have been studied using first principles calculations. These are done using the density-functional perturbation theory (DFPT) within the local density approximation (LDA) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (omega(TO) and omega(LO)), the high-frequency dielectric coefficient (epsilon(infinity)) and the dynamic effective charge (Z*) as a function of the composition (x). We found that the omega(TO) and omega(LO) follow a quadratic law in x and agree well with the experiment which proves that the VCA is a reliable method for mixed modes determination (2 bonds-1 mode). The obtained epsilon(infinity) and Z* have a quadratic form with x. We have also predicted the behavior of the optical and acoustical phonons with x at the high symmetry point X and L.