$\textit{Ab initio}$ anharmonic thermodynamic properties of cubic CaSiO$_3$ perovskite

TL;DR

This paper uses advanced ab initio methods to accurately compute the anharmonic thermodynamic properties of cubic CaSiO$_3$ perovskite, relevant for Earth's lower mantle conditions.

Contribution

It introduces a phonon quasiparticle approach to capture full anharmonicity and calculate free energies for strongly anharmonic materials at high pressures and temperatures.

Findings

Demonstrates anharmonic effects on thermodynamic properties

Provides a framework for phase boundary exploration

Calculates the thermal equation of state for cubic CaSiO$_3$

Abstract

We present an $\textit{ab initio}$ study of the thermodynamic properties of cubic CaSiO$_3$ perovskite (CaPv) over the pressure and temperature range of the Earth's lower mantle. We compute the anharmonic phonon dispersions throughout the Brillouin zone by utilizing the phonon quasiparticle approach, which characterizes the intrinsic temperature dependence of phonon frequencies and, in principle, captures full anharmonicity. Such temperature-dependent phonon dispersions are used to calculate $\textit{ab initio}$ free energy in the thermodynamic limit ($N \rightarrow \infty$) within the framework of the phonon gas model. Accurate free energy calculations enable us to investigate cubic CaPv's thermodynamic properties and thermal equation of state, where anharmonic effects are demonstrated. The present methodology provides an important theoretical approach for exploring phase boundaries, thermodynamic, and thermoelastic properties of strongly anharmonic materials at high pressures and temperatures.