Predicting the Mobility Increase of Coarse-Grained Polymer Models from Excess Entropy Differences.

We cast the acceleration of the dynamics of coarse-grained polymer models, or, conversely, the decrease in monomer friction in terms of excess entropy differences between different coarse-grained resolutions. From a simple bead-spring model of unentangled polymers in a melt, we systematically derive two coarse-grained models of different resolutions, for which exact excess entropies are obtained through a carefully carried out two-step thermodynamic integration. We found that the excess entropy differences between the coarser and finer models correlated well with the logarithm of the ratio of dynamical properties quantifying the acceleration upon changing the model resolution. Moreover, we have considered how well the two-body approximation to the excess entropy is correlated and also the scaling of the excess entropy in the analysis. Our results indicate that the acceleration brought about by coarse-graining can be understood in terms of excess entropy differences for unentangled polymers also. The correlations presented in this work may open new possibilities to a posteriori correct the coarse-graining dynamics by a simple route.