Anharmonic properties from a generalized third order ab~initio approach: theory and applications to graphite and graphene

TL;DR

This paper introduces a generalized ab initio method to calculate anharmonic phonon interactions, applied to graphite and graphene, revealing detailed phonon broadening behaviors and their impact on thermal conductivity.

Contribution

The authors develop a generic 2n+1 theorem-based approach within density functional perturbation theory to compute anharmonic scattering coefficients for phonons with arbitrary wavevectors.

Findings

Phonon broadening in graphite and graphene shows nonuniform features with sudden steps.

The acoustic branches in graphene exhibit nonzero broadening at small wavevectors at finite temperature.

Thermal conductivity calculations align with experiments out-of-plane but underestimate in-plane values.

Abstract

We have implemented a generic method, based on the 2n+1 theorem within density functional perturbation theory, to calculate the anharmonic scattering coefficients among three phonons with arbitrary wavevectors. The method is used to study the phonon broadening in graphite and graphene mono- and bi-layer. The broadening of the high-energy optical branches is highly nonuniform and presents a series of sudden steps and spikes. At finite temperature, the two linearly dispersive acoustic branches TA and LA of graphene have nonzero broadening for small wavevectors. The broadening in graphite and bi-layer graphene is, overall, very similar to the graphene one, the most remarkable feature being the broadening of the quasi acoustical ZO' branch. Finally, we study the intrinsic anharmonic contribution to the thermal conductivity of the three systems, within the single mode relaxation time approximation. We find the conductance to be in good agreement with experimental data for the out-of-plane direction but to underestimate it by a factor 2 in-plane.