Dynamic stabilization of cubicCaSiO3perovskite at high temperatures and pressures fromab initiomolecular dynamics

Abstract

The stability of cubic $\mathrm{Ca}\mathrm{Si}{\mathrm{O}}_{3}$ perovskite (CaPv) at high temperatures and pressures is investigated by vibrational normal-mode analysis. We compute power spectra of mode autocorrelation functions using a recently developed hybrid approach combining ab initio molecular dynamics with lattice dynamics. These power spectra, together with the probability distributions of atomic displacements, indicate that cubic CaPv is stabilized at $T\ensuremath{\sim}600$ K and $P\ensuremath{\sim}$ 26 GPa. We then utilize the concept of phonon quasiparticles to characterize the vibrational properties of cubic CaPv at high temperature and obtain anharmonic phonon dispersions through the whole Brillouin zone. Such temperature-dependent phonon dispersions pave the way for more accurate calculations of free-energy, thermodynamic, and thermoelastic properties of cubic CaPv at Earth's lower mantle conditions.