A new methodology for the extraction of anharmonic force constants from first principles density functional calculations

TL;DR

This paper introduces a novel method to extract both harmonic and anharmonic force constants from first principles calculations using small supercells and symmetry considerations, applicable to various materials.

Contribution

It presents a new approach that accurately determines anharmonic force constants from first principles, improving upon previous methods by utilizing symmetry and requiring small supercells.

Findings

Validated with Lennard-Jones potential where forces are exact

Applied to silicon in diamond structure, comparing to previous harmonic FCs

Demonstrated ability to extract anharmonic FCs up to any neighbor shell

Abstract

A new method for extracting force constants (FC) from first principles is introduced. It requires small supercells but very accurate forces. In principle, provided that forces are accurate enough, it can extract harmonic as well as anharmonic FCs up to any neighbor shell. Symmetries of the FCs as well as those of the lattice are used to reduce the number of parameters to be calculated. Results are illustrated for the case of Lennard-Jones potential where forces are exact and FCs can be calculated analytically, and Si in the diamond structure. The latter are compared to previously calculated harmonic FCs.