Solvent Free Ionic Solution Models from Multiscale Coarse-Graining

Solvent free models for aqueous ionic solutions are derived using the multiscale coarse-graining (MS-CG) method to obtain many-body potentials of mean force and generalized Langevin equations to propagate the model in time. The resulting models are compared to other implicit solvent models for aqueous NaCl in terms of both sampling efficiency and accuracy. First, the equilibrium structural properties of the models are compared, and then the temperature dependence of the interion potentials of mean force are determined to obtain the pairwise entropy associated with the effective ionic interactions. After validating the equilibrium behavior of the new models, the dynamical properties are investigated using generalized Langevin equation dynamics simulations. The dynamical properties can be put into better agreement with the original atomistic models by introducing an exponential memory kernel to account for the strong coupling between the ions and their water solvation shells.