Combined coarse-grained and atomistic simulation of liquid bisphenol A-polycarbonate: Liquid packing and intramolecular structure

We present a new coarse-graining scheme for efficient molecular dynamics simulations of polycarbonate liquids and compare its effectiveness to that of a previously presented model which uses a different coarse-grained representation. The effect of more realistically accounting for the excluded volume of the phenylene comonomeric units in the coarse-grained simulation is examined. The new treatment avoids artifacts arising from sphere-packing, which dominate the liquid structure and dynamics in the older scheme, leading to a significant improvement in the equilibration time, for systems run at the typical processing temperature of 570 K. However, we observe only a slight improvement (10(-4) eV/atom) in the equilibration of atomistically detailed samples that are inverse-mapped from the equilibrated coarse-grained configurations. Distributions in the atomistically resolved backbone bond and torsion angles are identical using the two schemes, as are computed liquid coherent scattering functions. This indicates that artifacts present at the coarsened level are effectively erased by equilibration at full-blown atomistic resolution, at least for systems with relatively short chains well above the glass transition temperature.