Effect of covalency,zero-point energy and charge transfer on the phase-transition,elastic and thermophysical properties of Ca-chalcogenides under compression

The pressure induced phase-transition, elastic and thermophysical properties of Ca-chalcogenides have been investigated by means of many body potential. The modified charge transfer potential consists of long-range Coulomb and charge-transfer interactions modified by covalency and short-range overlap repulsion extended up to second neighbours and zero-point energy effects. Another charge-transfer model excludes covalency and zero-point energy effects. These chalcogenides undergo first-order phase-transition at P _T = 39.23, 36.30 and 31.20 GPa and their equation of state show volume collapse of 10.12, 7.61 and 4.55% for CaS, CaSe and CaTe, respectively, which are in good agreement with the experiments. The elastic and thermophysical properties of these compounds have also been computed at normal and high pressures. Both the models are capable of explaining the Cauchy-discrepancy (C₁₂ ≠ C₄₄), elastic, phase-transition and thermophysical properties successfully.