Stability of the high-pressure phases of CaTiO3 perovskite at finite temperatures

The thermodynamic stability of the Pnma structure of CaTiO3 has been studied using hybrid density functional theory and Gibbs free energy calculations, including anharmonic effects. The use of the screened Heyd-Scuseria-Ernzerhof (HSE06) functional shifts the room temperature transition pressure from perovskite to post-perovskite structure by around 18 GPa, or 37%, compared with GGA-PBE. Both the lattice dynamics and choice of exchange functional play a significant role in stabilizing the Pnma structure at finite temperature. The Pnma structure is found to be stable up to 65 GPa at 300 K, consistent with the recent experimental observation of stable Pnma up to 60 GPa.