Effective force coarse-graining.

An effective force coarse-graining (EF-CG) method is presented in this paper that complements the more general multiscale coarse-graining (MS-CG) methodology. The EF-CG method determines effective pairwise forces between coarse-grained sites by averaging over the atomistic forces between the corresponding atomic groups in configurations sampled from equilibrium all-atom molecular dynamics simulations. The EF-CG method extracts the transferable part of the MS-CG force field at the cost of reduced accuracy in reproducing certain structural properties. Therefore, the EF-CG method provides an alternative to the MS-CG approach for determining CG force fields that give improved transferability but reduced structural accuracy. The EF-CG method is especially suitable for coarse-graining large molecules with high symmetry, such as bulky organic molecules, and for studying complex phenomena across a range of thermodynamic conditions. The connection between the EF-CG and MS-CG approaches as well as the limitations of the EF-CG method are also discussed. Numerical results for neopentane, methanol and ionic liquid systems illustrate the utility of the method.