Modeling non-harmonic behavior of materials from experimental inelastic neutron scattering and thermal expansion measurements

TL;DR

This paper develops a thermodynamic framework to quantify non-harmonic vibrational behavior in materials using experimental data, aiding the benchmarking of theoretical models of thermal properties.

Contribution

It introduces a method to derive non-harmonic vibrational quantities from experimental measurements, facilitating comparison with first-principles predictions.

Findings

Good agreement with literature data for aluminum and FeSi.

Provides an efficient approach to estimate anharmonic effects.

Quantifies harmonic, dilational, and anharmonic contributions to thermodynamic properties.

Abstract

Based on thermodynamic principles, we derive expressions quantifying the non-harmonic vibrational behavior of materials, which are rigorous yet easily evaluated from experimentally available data for the thermal expansion coefficient and the phonon density of states. These experimentally- derived quantities are valuable to benchmark first-principles theoretical predictions of harmonic and non-harmonic thermal behaviors using perturbation theory, ab initio molecular-dynamics, or Monte-Carlo simulations. We illustrate this analysis by computing the harmonic, dilational, and anharmonic contributions to the entropy, internal energy, and free energy of elemental aluminum and the ordered compound FeSi over a wide range of temperature. Results agree well with previous data in the literature and provide an efficient approach to estimate anharmonic effects in materials.