Origin of the improved fit of dynamical thermal conductivity using frequency-dependent lifetimes

Ascertain the physical mechanism responsible for the superior agreement obtained when fitting the dynamical lattice thermal conductivity with a frequency-dependent phonon lifetime, as opposed to a constant-lifetime Drude model, within the Green–Kubo and perturbative limits considered.

Background

The authors analyze the AC (dynamical) lattice thermal conductivity and attempt Drude-model fits. They find that a constant relaxation time provides a poor fit, whereas introducing a frequency-dependent lifetime (e.g., proportional to 1/ν) markedly improves agreement with calculations.

They examine two possible explanations—frequency dependence of the phonon self-energy and the role of auxiliary functions in their perturbative expression—but these do not account for the improved fit, leaving the underlying reason unresolved.