A second generation of mapping/reverse mapping of coarse-grained and fully atomistic models of polymer melts

Abstract

Recently the rotational isomeric state model for unperturbed polymers has been combined with potential energy functions designed for the description of the interactions of pairs of molecules in the gaseous state for the purpose of reversibly bridging between simulations of coarse-grained (on-lattice) and fully atomistic (in continuous space) models of polymers. The first generation of this method is reviewed here. This method has been applied to the conformation, energetics, structure, and dynamics of melts, free-standing thin films, and fibers, as well as to the cohesion of two thin films. Then the second generation is presented for the first time. When applied to a polyethylene melt, the first generation method maps every second carbon atom of the chains onto a high coordination lattice, which is derived from a diamond lattice. Physical densities are obtained with occupancies of about 1/6 of the sites on the high coordination lattice. The second generation utilizes every fourth carbon atom in the chains, and requires occupancy of only 1/12 of the sites. The short-range intramolecular interactions are controlled by an adaptation of the classic rotational isomeric state model for polyethylene, and the intermolecular interactions come from a discretization of a continuous Lennard-Jones potential, designed for the description of the interaction of pairs of hydrocarbons with 2 or 4 carbon atoms, for the first and second generation, respectively. Reversibility is demonstrated between the first-and second-generation models. In view of the prior demonstration of recovery of the fully atomistic model in continuous space from the first generation model, reversible interconversion of the first and second generation models demonstrates that the latter model can be reverse-mapped to the fully atomistic model in continuous space.