First Principles Study of Structural Phase Transition in Ag2S under High Pressure

We have studied the structural behavior of Ag2S under pressure (P) using density functional theory (DFT). By comparing the enthalpy differences of the different structures under pressure it can be seen that at zero pressure, the lowest energy structure calculated for Ag2S was the same as that found experimentally at low temperatures, namely, P2(1)/c monoclinic. While up to pressure above P = 30 GPa, Ag2S undergoes two different first-order structural phase transitions. The first one that observed at P = 9.3 GPa is from monoclinic P2(1)/c (phase I) structure to orthorhombic (phase II) P2(1)2(1)2(1) structure and the second transition at P = 13.8 GPa is computable to transition from orthorhombic P2(1)2(1)2(1) to monoclinic (phase III) P2(1)/c structure.