The phase transition, and elastic and thermodynamic properties of CaS derived fromfirst-principles calculations

Abstract

First-principles calculations of the crystal structures, phase transition, and elasticproperties of B1–B2 phase calcium sulfide (CaS) have been carried out with the plane-wavepseudopotential density functional theory method. The calculated values (for crystal structuresand the phase transition) are in very good agreement with experimental data as well aswith some of the existing model calculations. The dependence of the elastic constantscij, the aggregate elastic modulus, the deviation from the Cauchy relation, and the elasticanisotropy on pressure have been investigated. The normalized elastic constantscij′ have been introduced to investigate the elasticity of CaS in detail. Moreover, the variation of thePoisson ratio, Debye temperature, and longitudinal and transverse elastic wave velocity with pressureP up to 70 GPa at 0 K have been investigated for the first time.