A structure-based coarse-grained model for polymer melts

In this study we explore a systematic procedure to coarsen a microscopic mo del towards a mesoscopic model. The procedure is applied to a system of cha ins of ten beads, representing a low molecular weight polymer melt. Our met hod consists of defining coarse-grained sites in the microscopic system, an d calculating their spatial distribution on the pair level. The effective i nteraction between the coarse-grained sites is then obtained by bringing th e pair interaction in consistence with the pair density. We investigate bot h a dynamic and a stochastic method for this step. The so obtained mesoscop ic interaction is used in a molecular dynamics simulation to investigate th e pressure of the coarse-grained system. We found that the pair interaction that reproduces the pair density predicts a pressure that is significantly lower than the microscopic value, even if we take the state-dependency of the coarse-grained interactions into account. We therefore conclude that co arse-grained models lack thermodynamic consistency. (C) 2001 American Insti tute of Physics.