# Anharmonic interatomic force constants and thermal conductivity from Gr\"{u}neisen parameters: an application to graphene

## TL;DR

This paper introduces a novel, less computationally intensive method to estimate dominant anharmonic interatomic force constants and thermal conductivity in materials like graphene using Gr"uneisen parameters derived from phonon frequency shifts.

## Contribution

The authors propose a new approach to determine the largest cubic IFCs from Gr"uneisen parameters, enabling approximate thermal conductivity calculations with reduced computational cost.

## Key findings

- Accurately estimates dominant cubic IFCs in graphene.
- Achieves reasonable agreement with DFT results for thermal conductivity.
- Provides a pedagogical framework for analyzing Gr"uneisen parameters in two-band models.

## Abstract

Phonon-mediated thermal conductivity, which is of great technological relevance, fundamentally arises due to anharmonic scattering from interatomic potentials. Despite its prevalence, accurate first-principles calculations of thermal conductivity remain challenging, primarily due to the high computational cost of anharmonic interatomic force constant (IFCs) calculations. Meanwhile, the related anharmonic phenomenon of thermal expansion is much more tractable, being computable from the Gr\"uneisen parameters associated with phonon frequency shifts due to crystal deformations. In this work, we propose a novel approach for computing the largest cubic IFCs from the Gr\"uneisen parameter data. This allows an approximate determination of the thermal conductivity via a much less expensive route. The key insight is that although the Gr\"uneisen parameters cannot possibly contain all the information on the cubic IFCs, being derivable from spatially uniform deformations, they can still unambiguously and accurately determine the largest and most physically relevant ones. By fitting the anisotropic Gr\"uneisen parameter data along judiciously designed deformations, we can deduce (i.e., reverse engineer) the dominant cubic IFCs and estimate three-phonon scattering amplitudes. We illustrate our approach by explicitly computing the largest cubic IFCs and thermal conductivity of graphene, especially for its out-of-plane (flexural) modes that exhibit anomalously large anharmonic shifts and thermal conductivity contributions. Our calculations on graphene not only exhibits reasonable agreement with established DFT results, but also presents a pedagogical opportunity for introducing an elegant analytic treatment of the Gr\"uneisen parameters of generic two-band models. Our approach can be readily extended to more complicated crystalline materials with nontrivial anharmonic lattice effects.