Understanding Divergent Thermal Conductivity in Single Polythiophene Chains using Modal Analysis and Sonification

TL;DR

This study combines molecular dynamics, modal analysis, and sonification to identify the low-frequency transverse vibrations in polythiophene chains as the cause of divergent thermal conductivity, highlighting persistent mode correlations.

Contribution

It introduces a novel combination of Green-Kubo Modal Analysis and sonification to pinpoint the modes responsible for thermal conductivity divergence in polythiophene chains.

Findings

Low-frequency transverse vibrations (~0.05 THz) dominate thermal conductivity.

Divergence arises from persistent correlations among the three lowest frequency modes.

Sonification reveals sinusoidal heat flux envelopes linked to divergence.

Abstract

We used molecular dynamics simulations, the Green-Kubo Modal Analysis (GKMA) method and sonification to study the modal contributions to thermal conductivity in individual polythiophene chains. The simulations suggest that it is possible to achieve divergent thermal conductivity and the GKMA method allowed for exact pinpointing of the modes responsible for the anomalous behavior. The analysis showed that transverse vibrations in the plane of the aromatic rings at low frequencies ~ 0.05 THz are primarily responsible. Further investigation showed that the divergence arises from persistent correlation between the three lowest frequency modes on chains. Sonification of the mode heat fluxes revealed regions where the heat flux amplitude yields a somewhat sinusoidal envelope with a long period similar to the relaxation time. This characteristic in the divergent mode heat fluxes gives rise to the overall thermal conductivity divergence, which strongly supports earlier hypotheses that attribute the divergence to correlated phonon-phonon scattering/interactions.