Lattice Thermal Transport and Phonon-Phonon Coupling from First Principles

Abstract

Lattice component represents the most important contribution to thermal transport in a large group of materials. A quantitative description of the lattice thermal conductivity requires an understanding on the microscopic phonon-phonon coupling. Inelastic neutron scattering (INS) can be utilized to measure phonon power spectra across the Brillouin zone, however, it can only be performed in a few neutron sources. Large size single crystal samples, which can be challenging to grow for some materials, are also required for phonon dispersion measurements, making it even more difficult to study the phonon coupling from experiments. Theoretical investigation provides an alternative mean for an in-depth understanding on lattice dynamics, nonetheless, conventional approaches are usually based on the harmonic approximation, in which phonons are assumed to be non-interacting quasi-particles. We have studied the strain effects on the thermal transport of two dimensional BN based on first-principles anharmonic force constant calculations. To the lowest order in perturbation theory, phonon power spectra were calculated to unveil the microscopic origins of the strain effects. In addition, we have also investigated the anharmonic phonon spectra of bulk crystals from molecular dynamics; excellent agreements between simulations and INS measurements have been obtained.