Temperature dependent effective third order interatomic force constants from first principles

TL;DR

This paper extends the TDEP method to include third order interatomic force constants, enabling accurate finite-temperature phonon lifetime calculations from first principles, demonstrated on silicon and epsilon-FeSi.

Contribution

The paper introduces a generalized TDEP approach that incorporates third order force constants from ab initio MD simulations at finite temperature.

Findings

Successful calculation of Mode Grüneisen parameters for Si.

Efficient phonon lifetime calculations for Si and epsilon-FeSi.

Demonstration of temperature-induced phonon softening in epsilon-FeSi.

Abstract

The temperature dependent effective potential (TDEP) method is generalized beyond pair interactions. The second and third order force constants are determined consistently from ab initio molecular dynamics simulations at finite temperature. The reliability of the approach is demonstrated by calculations of the Mode Gr\"uneisen parameters for Si. We show that the extension of TDEP to higher order allows for an efficient calculation of the phonon life time, in Si as well as in $\epsilon$-FeSi, a system that exhibits anomalous softening with temperature.