High pressure polymorph of CdS predicted by first principles

Ab initio phonon calculations on CdS are performed to probe the high pressure structural behaviors. We predicted an unstable transverse acoustic (TA) mode for NaCl-CdS (B1) and a phase transition of B1→Pmmn driven by this soft mode is thus identified, excluding probable high pressure Cmcm phase. Furthermore, a softening TA phonon mode at the zone boundary M point of CsCl-CdS (B2) is predicted, which results in the phase transition from Pmmn to tetrahedral P4/nmm (B10). Enthalpy calculation reveals that Pmmn phase becomes energetically more favorable than the B1 phase over 51.2 GPa, and B10 phase is stable in a pressure range of 80.3–85.5 GPa, above which B10 phase will decompose into Cd and S.