Thermal conductivity and transport modes in glassy GeTe4 by first-principles molecular dynamics

First-principles molecular dynamics is employed to investigate thermal transport in glassy ${\mathrm{GeTe}}_{4}$, a subsystem of several ternary phase-change materials. As a first result, we found modes localized on a few atoms in the vibrational density of states. The thermal transport is further rationalized by calculating the thermal conductivity for a range of system sizes and shapes via the approach-to-equilibrium methodology. By considering the length dependence of the thermal conductivity, we provide evidence of propagative modes with mean free paths as long as 6 nm, i.e., well beyond short-range order distances. Extrapolation of our bulk thermal conductivity to macroscopic sizes is in full agreement with the experimental values. Finally, we assess phenomenological models developed for the thermal conductivity of disordered materials by enriching their intrinsic significance via the insertion in their analytical expression of values obtained via first-principles molecular dynamics.