Thermal Expansion in Insulating Solids From First Principles

TL;DR

This paper reviews how to use first-principles density functional theory and the quasiharmonic approximation to predict thermal expansion in insulating solids, providing practical guidance and examples.

Contribution

It offers a comprehensive tutorial on applying DFT and quasiharmonic approximation to calculate thermal expansion, including phonon analysis and Gr"uneisen parameters, with examples on silicon and PbTiO$_3$.

Findings

Validated the method with silicon data

Demonstrated anisotropic expansion in PbTiO$_3$

Compared theoretical predictions with experimental results

Abstract

In this Tutorial, we describe the use of the quasiharmonic approximation and first-principles density functional theory (DFT) to calculate and analyze the thermal expansion of insulating solids. We discuss the theory underlying the quasiharmonic approximation, and demonstrate its practical use within two common frameworks for calculating thermal expansion: the Helmholtz free energy framework and Gr\"{u}neisen theory. Using the example of silicon, we provide a guide for predicting how the lattice parameter changes as a function of temperature using DFT, including the calculation of phonon modes and phonon density of states, elastic constants, and specific heat. We also describe the calculation and interpretation of Gr\"{u}neisen parameters, as well as how they relate to coefficients of thermal expansion. The limitations of the quasiharmonic approximation are briefly touched on, as well as the comparison of theoretical results with experimental data. Finally, we use the example of ferroelectric PbTiO$_3$ to illustrate how the methods used can be adapted to study anisotropic systems.