Comparing simulated specific heat of liquid polymers and oligomers to experiments

Abstract

The specific heat is a central property of condensed matter systems including polymers and oligomers in their condensed phases. Yet, predictions of this quantity from molecular simulations and successful comparisons to experimental data are scarce if existing at all. One reason for this may be that the internal energy and thus the specific heat cannot be coarse-grained so that they defy their rigorous computation with united-atom models. Moreover, many modes in a polymer barely contribute to the specific heat because of their quantum mechanical nature. Here, we demonstrate that an analysis of the mass-weighted velocity autocorrelation function allows specific heat predictions to be corrected for quantum effects so that agreement with experimental data is on par with predictions of other routinely computed quantities. We outline how to construct corrections for both all-atom and united-atom descriptions of chain molecules. Corrections computed for eleven hydrocarbon oligomers and commodity polymers deviate by less than $k_\textrm{B}/10$ within a subset of nine molecules. Our results may benefit the prediction of heat conductivity.