Impact of anharmonicity on sound wave velocities at extreme conditions

TL;DR

This paper investigates how anharmonic atomic vibrations influence the calculation of sound wave velocities in materials under extreme conditions, aiming to improve agreement between theoretical predictions and experimental data, especially for Earth's core materials.

Contribution

It introduces a method to incorporate anharmonic effects into ab initio calculations of sound velocities, addressing discrepancies with experimental results at extreme conditions.

Findings

Anharmonic effects significantly impact sound velocity calculations.

Inclusion of anharmonicity improves agreement with experimental data.

The approach is particularly relevant for modeling Earth's inner core materials.

Abstract

Theoretical calculations of sound-wave velocities of materials at extreme conditions are of great importance to various fields, in particular geophysics. For example, the seismic data on sound-wave propagation through the solid iron-rich Earth's inner core have been the main source for elucidating its properties and building models. As the laboratory experiments at very high temperatures and pressures are non-trivial, ab initio predictions are invaluable. The latter, however, tend to disagree with experiment. We notice that many attempts to calculate sound-wave velocities of matter at extreme conditions in the framework of quantum-mechanics based methods have not been taking into account the effect of anharmonic atomic vibrations. We show how anharmonic effects can be incorporated into ab initio calculations and demonstrate that in particular they might be non-negligible for iron in Earth's core. Therefore, we open an avenue to reconcile experiment and ab initio theory.