quasiharmonic equations of state for dynamically-stabilized soft-mode materials

TL;DR

This paper develops a quasiharmonic approach to model soft-mode materials, enabling the prediction of phase transitions like B1--B2 in solid periclase under high pressure and temperature conditions.

Contribution

It introduces a novel method for incorporating soft modes into quasiharmonic equations of state using a double-well energy model, validated with density-functional calculations.

Findings

Predicted B1--B2 phase transition in periclase at high pressures and temperatures.

Developed a harmonic-fitting approach for soft-mode energy relations.

Applied statistical physics to enhance quasiharmonic modeling.

Abstract

We introduce a method for treating soft modes within the analytical framework of the quasiharmonic equation of state. The corresponding double-well energy-displacement relation is fitted to a functional form that is harmonic in both the low- and high-energy limits. Using density-functional calculations and statistical physics, we apply the quasiharmonic methodology to solid periclase. We predict the existence of a B1--B2 phase transition at high pressures and temperatures.