Equations of state and stability of MgSiO$_3$ perovskite and post-perovskite phases from quantum Monte Carlo simulations

TL;DR

This study uses quantum Monte Carlo and DFT calculations to accurately determine the equations of state and phase boundary of MgSiO$_3$ in Earth's lower mantle conditions, improving upon previous models.

Contribution

It provides the first QMC-based equations of state for MgSiO$_3$ phases, offering more accurate phase boundary predictions than prior LDA and GGA methods.

Findings

QMC results agree well with experimental data

Phase boundary matches experimental observations

Improved accuracy over GGA and LDA calculations

Abstract

We have performed quantum Monte Carlo (QMC) simulations and density functional theory (DFT) calculations to study the equations of state of MgSiO$_3$ perovskite (Pv) and post-perovskite (PPv), up to the pressure and temperature conditions of the base of Earth's lower mantle. The ground state energies were derived using QMC and the temperature dependent Helmholtz free energies were calculated within the quasi-harmonic approximation and density functional perturbation theory. The equations of state for both phases of MgSiO$_3$ agree well with experiments, and better than those from generalized gradient approximation (GGA) calculations. The Pv-PPv phase boundary calculated from our QMC equations of states is also consistent with experiments, and better than previous LDA calculations. We discuss the implications for double crossing of the Pv-PPv boundary in the Earth.