Interpretation of apparent thermal conductivity in finite systems from equilibrium molecular dynamics simulations

TL;DR

This paper clarifies how to interpret apparent thermal conductivity in finite systems from equilibrium molecular dynamics simulations, showing it relates to nonperiodic boundary NEMD results and addressing the decay of heat current autocorrelation.

Contribution

It introduces a method to accurately interpret finite-system thermal conductivity from EMD by comparing with NEMD, accounting for boundary effects and autocorrelation decay.

Findings

Maximum EMD thermal conductivity equals NEMD conductivity at half the domain length.

Negative autocorrelation values develop after a certain correlation time.

Efficacious link established between EMD and NEMD for finite samples.

Abstract

We propose a way to properly interpret the apparent thermal conductivity obtained for finite systems using equilibrium molecular dynamics simulations (EMD) with fixed or open boundary conditions in the transport direction. In such systems the heat current autocorrelation function develops negative values after a correlation time which is proportional to the length of the simulation cell in the transport direction. Accordingly, the running thermal conductivity develops a maximum value at the same correlation time and eventually decays to zero. By comparing EMD with nonequilibrium molecular dynamics (NEMD) simulations, we conclude that the maximum thermal conductivity from EMD in a system with domain length 2L is equal to the thermal conductivity from NEMD in a system with domain length L. This facilitates the use of nonperiodic-boundary EMD for thermal transport in finite samples in close correspondence to NEMD.