(561i) Refinement of Coarse-Grained Bonded Potential Dynamics in Chemically-Specific Molecular Dynamics Models of Polymers

In coarse-grained (CG) models, many atoms are lumped into larger units to eliminate "fast" degrees of freedom whose size scales are small to enable simulation of larger systems at longer timescales. In recent work [J. Chem. Phys. 154,084114 (2021)], we studied a CG model that aims to preserve both chemical specificity and dynamics of a polymer melt. We used iterative Boltzmann inversion (IBI) to parameterize the conservative potential to reproduce the structure of the melt from all-atom (AA) reference simulations, and Langevin dynamics to introduce a dissipative potential as a means to recover the AA dynamics. Here we further our analysis of CG models by examining the influence of bonded potential dynamics on CG property predictions. In IBI, CG potentials are parametrized such that the bonded and pair distributions match the target structural distributions of the AA reference system. However, deeper analysis shows that even after correction with the Langevin potential to match diffusion properties of the chains, the dynamics of the CG potentials are still much faster the AA target potential dynamics. This indicates that this could be another handle in which to further refine and tune the CG potential. Information from the literature based on comparison of the dynamics of AA and United Atom (UA) models reinforces this idea. To begin our analysis, we first devise measures based on autocorrelation functions to quantify the dynamics of the CG and AA reference bonded potentials. It is shown that time rescaling factors can be computed that result in a better overall match of dynamics for the two cases, although the exact features may be impossible to match. Finally, we examine approaches to refine the IBI bonded potentials to better match the AA dynamics while preserving the fluid structure based on IBI. The effect of the refined potentials on property predictions both with and without Langevin dynamics are analyzed.