Systematic Coarse-Graining of Polymeric Systems Using Soft Potentials

Full atomistic or united atom simulations of multi-chain systems are not feasible at present due to their formidable computational requirements. Molecular simulations with coarse-grained models where each segment represents the center-of-mass of a group of atoms/monomers have to be used instead. While atoms or monomers interact with hard excluded-volume interactions (e.g., the Lennard-Jones potential) and cannot overlap, the coarse-grained segments can certainly overlap and should therefore interact with soft potentials that allow complete particle overlapping. Coarse-grained models, however, reduce the chain conformational entropy, which plays an essential role in the thermodynamic behavior of polymeric systems. Furthermore, when molecules of different sizes present (e.g., polymers in a small-molecule solvent), it is equally important to correctly describe the translational entropy (size ratio) of different molecules in coarse-grained models. In this talk we address the problem of how to obtain such soft potentials and the appropriate criteria for coarse-graining both in continuum and on a lattice.