Transferability of Nonbonded Interaction Potentials for Coarse-Grained Simulations: Benzene in Water.

Methods to parametrize coarse-grained simulation models for molecular fluids frequently either attempt to match the fluid structure (e.g., pair correlation functions) previously obtained with detailed atomistic models or aim at reproducing macroscopically observable thermodynamic properties. In either case, the coarse-grained models are state-point-dependent, and it is unclear to what extent the models obtained at a given state point are transferable, for example, to different compositions in the case of solution mixtures. Usually, it remains unclear as well whether structure-based potentials reproduce macroscopic thermodynamic properties and, vice versa, if thermodynamics-based potentials reproduce microscopic structural properties. In this paper, we use the Kirkwood-Buff theory of solutions in order to link local structural information and thermodynamic properties sampled with structure-based potentials. We investigate benzene/water mixtures at varying concentrations as a model hydrophobic/hydrophilic system and study the transferability of a coarse-grained model that describes the water and benzene molecules as single interaction sites. The coarse-grained model, parametrized at a high aqueous dilution of benzene, reproduces the Kirkwood-Buff integrals of mixtures obtained with the detailed-atomistic model, and it reproduces the change in the benzene chemical potential with composition up to the concentration of thermodynamic instability. The observed transferability of the potential supports the idea that hydrophobic interactions between small molecules are pairwise additive.