Lattice thermal transport from phonon spectra beyond perturbation theory

TL;DR

This paper introduces a molecular dynamics method to compute phonon spectral densities beyond perturbation theory, accurately capturing thermal transport in anharmonic materials.

Contribution

It develops a framework linking classical molecular dynamics with quantum heat transport, extending analysis to strongly anharmonic systems.

Findings

Method accurately reproduces phonon spectra beyond perturbation theory.

Thermal conductivity results agree well with experimental data.

Applicable to both harmonic and anharmonic materials.

Abstract

We develop a molecular dynamics framework to compute the mode-resolved phonon spectral density from classical correlations of an annihilation-like phonon variable. For harmonic oscillators, classical molecular dynamics exactly reproduces the corresponding quantum Kubo-transformed correlator, providing the basis for extension to anharmonic systems. Using PbTe as a benchmark and Cs$_3$Bi$_2$I$_6$Cl$_3$ as a strongly anharmonic test case, we show that the method captures both quasiparticle and non-Lorentzian spectra beyond perturbative quasiparticle theory, while yielding thermal conductivity in good agreement with experiment. This framework provides a direct route from classical molecular dynamics to quantum-mechanical Wigner heat transport in solids.