Entropic Augmentation of Coarse-Grained Potentials for Resolving Dynamics Using the Iterative Boltzmann Inversion (IBI) Method

Recently, we studied an approach for coarse-grained (CG) molecular dynamics (MD) in which we used Iterative Boltzmann Inversion (IBI) in combination with Langevin dynamics to parametrize force-fields for polymers melts [J. Chem. Phys. 154, 084114 (2021); J. Phys. Chem. B, 127 (31), (2023)]. Here, we study the potential dynamics of this model to determine more precisely the effect of Langevin friction and use that as a basis for model improvement. Dynamic characterization of the intramolecular and pair potentials shows that here Langevin friction modifies only the pair dynamics in this formulation. Based on the hypothesis that the intramolecular potentials need similar entropic augmentation as Langevin provides for pair, we use simplification of GLE models for dynamic bond friction to derive friction-based models for dynamic correction of the bonded potentials. Pedagogically, the results show the virtual bonds in the CG space function as damped anharmonic oscillators where the enthalpic terms resolve the structural distributions and the frictional terms resolve dynamics. Indirect tests of the model are used to show that intramolecular forces are also an important factor in tuning the dynamics of IBI based CG models.