Understanding Divergent Thermal Conductivity in Single
Polythiophene Chains Using Green–Kubo Modal Analysis and Sonification
LvWei
WintersR. Michael
DeAngelisFreddy
WeinbergGil
HenryAsegun
2017
We used molecular
dynamics simulations and the Green–Kubo
modal analysis (GKMA) method as well as 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 in individual polythiophene chains of certain
lengths, with periodic boundary conditions. Application of the GKMA
method further 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 for the divergence. Within the integration
time, one mode in particular exhibits a thermal conductivity contribution
greater than 100 W m<sup>–1</sup> K<sup>–1</sup>. Further
investigation showed that the divergence arises from persistent correlation
between the three lowest frequency modes on chains that have exact
multiples of 30 unit cells in length. 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 as opposed to a lack of scattering/interaction
among modes (e.g., infinite relaxation time/ballistic transport).