# A fast anharmonic free energy method with an application to vacancies in ZrC

## TL;DR

This paper introduces a rapid and accurate method for calculating anharmonic free energies in crystals, demonstrated on ZrC with predictions on vacancy behavior and thermodynamics.

## Contribution

A novel computational approach that significantly accelerates anharmonic free energy calculations with high accuracy, applicable to complex materials.

## Key findings

- Achieves 10x speed-up over existing methods
- Predicts vacancy concentrations in ZrC_x
- Provides accurate heat capacity estimates

## Abstract

We propose an approach to calculate the anharmonic part of the volumetric-strain and temperature dependent free energy of a crystal. The method strikes an effective balance between accuracy and computational efficiency, showing a $\times10$ speed-up on comparable free energy approaches at the level of density functional theory, with average errors less than 1 meV/atom. As a demonstration we make new predictions on the thermodynamics of substoichiometric ZrC$_x$, including vacancy concentration and heat capacity.