An efficient ab-initio quasiharmonic approach for the thermodynamics of solids

TL;DR

The paper introduces the self-consistent quasiharmonic approximation (SC-QHA), a computationally efficient first-principles method for accurately calculating the thermodynamic properties of solids at finite temperatures, especially for complex structures.

Contribution

The SC-QHA method reduces phonon calculations compared to conventional QHA and enables analysis of thermal phenomena in complex and large structures.

Findings

SC-QHA matches experimental data for silicon, diamond, and alumina.

It effectively studies pressure effects on diamond and alumina.

It accurately computes properties of complex ferroelectric Ca$_3$Ti$_2$O$_7$.

Abstract

A first-principles approach called the {\it{self-consistent quasiharmonic approximation}} (SC-QHA) method is formulated to calculate the thermal expansion, thermomechanics, and thermodynamic functions of solids at finite temperatures with both high efficiency and accuracy. The SC-QHA method requires fewer phonon calculations than the conventional QHA method, and also facilitates the convenient analysis of the microscopic origins of macroscopic thermal phenomena. The superior performance of the SC-QHA method is systematically examined by comparing it with the conventional QHA method and experimental measurements on silicon, diamond, and alumina. It is then used to study the effects of pressure on the anharmonic lattice properties of diamond and alumina. The thermal expansion and thermomechanics of Ca$_3$Ti$_2$O$_7$, which is a recently discovered important ferroelectric ceramic with a complex crystal structure that is computationally challenging for the conventional QHA method, are also calculated using the formulated SC-QHA method. The SC-QHA method can significantly reduce the computational expense for various quasiharmonic thermal properties especially when there are a large number of structures to consider or when the solid is structurally complex. It is anticipated that the algorithm will be useful for a variety of fields, including oxidation, corrosion, high-pressure physics, ferroelectrics, and high-throughput structure screening when temperature effects are required to accurately describe realistic properties.