# Analysing heat transport in crystalline polymers in real and reciprocal space

## TL;DR

This paper compares real and reciprocal space methods for modeling heat transport in crystalline polymers, highlighting the importance of accurate models for different materials.

## Contribution

The study demonstrates the necessity of including higher-order anharmonicities for accurate thermal conductivity predictions in polyethylene.

## Key findings

- Consistent results are achieved using machine-learned potentials when material intricacies are considered.
- Higher-order anharmonicities are crucial for accurate thermal conductivity in polyethylene.
- Long-lived phonons at 11-16 THz complicate classical statistics in molecular dynamics approaches.

## Abstract

Heat transport can be modelled with a variety of approaches in real space (using molecular dynamics) or in reciprocal space (using the Boltzmann transport equation). Employing two conceptually different approaches of each type, we study heat transport in crystalline polyethylene and polythiophene. We find that consistent results can be obtained when using highly efficient and accurate machine-learned potentials, provided that the physical intricacies of the considered materials and methods are correctly accounted for. For polythiophene, this turns out to be comparably straightforward, whereas for polyethylene, we find that the inclusion of higher-order anharmonicities is crucial to avoid a massive overestimation of the thermal conductivity. The responsible long-lived phonons are found at relatively high frequencies between 11 THz and 16 THz. This complicates the use of classical statistics in all molecular-dynamics-based approaches.