Ab initio calculation of the elastic properties and the lattice dynamics of the ZnxCd1-xSe alloy

The lattice dynamics and elastic properties of the ternary ZnxCd1-xSe alloy have been studied using first-principle calculations. These are done using the density-functional perturbation theory (DFPT) within local density approximation (LDA) and employing 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)), the dynamic effective charge (Z*) and the elastic constants (C-11, C-12, C-44) 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. The obtained epsilon(infinity), Z*, C-11, C-12 and C-44 have a quadratic form with x. The elastic constant tensors for simple cubic eight-atom supercells with x = 0.25, 0.5 and 0.75 have been computed and are in good agreement with those obtained from VCA.