\textit{Ab initio} lattice thermal conductivity of MgSiO$_3$ across perovskite-postperovskite phase transition

TL;DR

This study uses ab initio simulations to compare the lattice thermal conductivity of MgSiO3 in perovskite and postperovskite phases under Earth's mantle conditions, revealing phase-dependent differences due to phonon properties.

Contribution

It provides the first detailed ab initio analysis of lattice thermal conductivity across the perovskite-postperovskite transition in MgSiO3 under mantle conditions.

Findings

MgPPv has ~25% higher thermal conductivity than MgPv in the lowermost mantle.

Higher phonon velocities in MgPPv are due to its smaller primitive cell.

Temperature and pressure significantly influence the thermal conductivities.

Abstract

Lattice thermal conductivity ($\kappa_{lat}$) of MgSiO$_3$ postperovskite (MgPPv) under the Earth's lower mantle high pressure-temperature conditions is studied using the phonon quasiparticle approach by combing \textit{ab initio} molecular dynamics and lattice dynamics simulations. Phonon lifetimes are extracted from the phonon quasiparticle calculations, and the phonon group velocities are computed from the anharmonic phonon dispersions, which in principle capture full anharmonicity. It is found that throughout the lowermost mantle, including the D" region, $\kappa_{lat}$ of MgPPv is ~25% larger than that of MgSiO$_3$ perovskite (MgPv), mainly due to MgPPv's higher phonon velocities. Such a difference in phonon velocities between the two phases originates in the MgPPv's relatively smaller primitive cell. Systematic results of temperature and pressure dependences of both MgPPv's and MgPv's $\kappa_{lat}$ are demonstrated.