Phase transition and optical properties ofCaCl2 under high pressure by ab initio pseudopotential plane-wave calculations

Abstract

We present a detailed investigation ofCaCl2 under highpressure in CaCl2 (Pnnm,Z = 2)and α-PbO2 (Pbcn, Z = 4) phases, respectively. Theoretical calculations are performed by using the ab initiopseudopotential plane-wave method based on the density functional method. We estimatethe transition pressure between the two phases by the crossing point of their enthalpies,which are equivalent to the Gibbs free energy at zero temperature, after optimizing thestructures under high pressure. Our results show that the transition happens at about2.9 GPa, which is in agreement with the experimental data. We calculate thestructural parameters, charge transfers, bond structures, density of states andoptical properties. The calculated results show that there are no charge transfers inCaCl2 structure under high pressure. It is found that the transitions from the Cl 3p to Ca 4s and Cl3s to Ca 3p orbitals contribute mainly to the dielectric function. The optical properties ofCaCl2 (Pnnm, Z = 2) do not vary much under pressure. However, some of the dispersion curves of optical constants in theα-PbO2 (Pbcn, Z = 4) phase are changed significantly under pressure.