Thermal conduction in molecular materials using coarse grain dynamics: Role of mass diffusion and quantum corrections for molecular dynamics simulations

We use a mesodynamical method, denoted dynamics with implicit degrees of freedom (DID), to characterize thermal transport in a model molecular crystal below and above its melting temperature. DID represents groups of atoms (molecules in this case) using mesoparticles and the thermal role of the intramolecular degrees of freedom (DoFs) are described implicitly using their specific heat. We focus on the role of these intramolecular DoFs on thermal transport. We find that thermal conductivity is independent of intramolecular specific heat for solid samples and a linear relationship between the two quantities in liquid samples with the coefficient of proportionality being the mass diffusivity of the mesoparticles. As the temperature of the liquids is increased, thermal conductivity exhibits an increased sensitivity with respect to the specific heat of the internal DoFs due to the enhanced molecular mobility. Based on these results, we propose a simple method to incorporate quantum corrections to thermal conductivity obtained from nonequilibrium molecular dynamics simulations of molecular liquids. Our results also provide insight into the development of thermally accurate coarse grain models of soft materials.