A Heavy Solution for Molecular Thermal Management: Phonon Transport Suppression with Heavy Atoms

Thermal management in molecular systems presents challenges that require a deeper understanding of phonon transport, an essential aspect of heat conduction in single molecule junctions. Our work introduces the use of heavy atoms as a strategy for suppressing phonon transport in organic molecules. Starting with a 1D force-constant model and density functional theory calculations of model chemical systems, we illustrate how increasing the mass of a central atom affects the phonon transmission and conductance. Following this, we turn our attention to the chemically accessible systems of metallapolyynes and extended metal atom chains (EMACs). Our findings suggest that several of the studied EMACs exhibit thermal conductance either near or below a recently proposed threshold of 10 pW/K – a crucial step towards reaching high thermoelec- tric figure of merits. Specifically, we predict that the molecule MoMoNi(npo)4 (NCS)2 has a thermal conductance of just 8.3 pW/K at 300 K. Our results demonstrate that conceptually simple chemical modifications can markedly reduce the thermal conductance of single molecules; these results both deepens our understanding of the mechanisms driving single-molecule phonon thermal conductance and suggest a path towards using single molecules as thermoelectric materials.