# Calculation of the Anisotropic Coefficients of Thermal Expansion: A First-Principles Approach

## TL;DR

This paper introduces a first-principles method that incorporates anharmonic effects to accurately predict anisotropic thermal expansion coefficients and other thermal properties of materials across wide temperature ranges.

## Contribution

The authors develop a novel computational approach that extends beyond quasiharmonic approximation to include anharmonic effects for thermal property prediction.

## Key findings

- Accurately predicts thermal expansion coefficients for Cu and AlN.
- Shows good agreement with experimental data over wide temperature ranges.
- Provides a comprehensive method for thermal property calculations in anisotropic materials.

## Abstract

Predictions of the anisotropic coefficients of thermal expansion are needed to not only compare to experimental measurement, but also as input for macroscopic modeling of devices which operate over a large temperature range. While most current methods are limited to isotropic systems within the quasiharmonic approximation, our method uses first-principles calculations and includes anharmonic effects to determine the temperature-dependent properties of materials. These include the lattice parameters, anisotropic coefficients of thermal expansion, isothermal bulk modulus, and specific heat at constant pressure. Our method has been tested on two compounds (Cu and AlN) and predicts thermal properties which compare favorably to experimental measurement over a wide temperature range.