Revealing molecule-internal mechanisms that control phonon heat transport through single-molecule junctions by a genetic algorithm

TL;DR

This study uses a genetic algorithm to systematically identify molecular structures that can control phonon heat transport in single-molecule junctions, revealing physical and chemical mechanisms that modulate thermal conductance.

Contribution

It introduces a genetic algorithm approach to explore chemical space for molecules with extreme thermal conductance and analyzes mechanisms affecting phonon transport.

Findings

Mechanisms to reduce phonon transport include linker choice, substituents, and internal twists.

High conductance molecules are typically uniform and chain-like.

Identified mechanisms are systematically classified across different theoretical levels.

Abstract

Measurements of the thermal conductance of single-molecule junctions have recently been reported for the first time. It is presently unclear, how much the heat transport can be controlled through molecule-internal effects. The search for molecules with lowest and highest thermal conductance is complicated by the gigantic chemical space. Here we describe a systematic search for molecules with a low or a high phononic thermal conductance using a genetic algorithm. Beyond individual structures of well performing molecules, delivered by the genetic algorithm, we analyze patterns and identify the different physical and chemical mechanisms to suppress or enhance phonon heat flow. In detail, mechanisms revealed to reduce phonon transport are related to the choice of terminal linker blocks, substituents and corresponding mass disorder or destructive interference, meta couplings and molecule-internal twist. For a high thermal conductance, the molecules should instead be rather uniform and chain-like. The identified mechanisms are systematically analyzed at different levels of theory, and their significance is classified. Our findings are expected to be important for the emerging field of molecular phononics.