Coarse-Grained Potential Model for Structural Prediction of Confined Water.

We propose a coarse-grained potential model to predict the concentration and potential profiles of confined water. In this model, we represent one water molecule with one coarse-grained bead, such that the interactions between the coarse-grained beads are given by isotropic two-body potentials. Due to the inherent inhomogeneity of the confined water microstructure, we find that a single spatially uniform coarse-grained water-water potential may not be sufficient to accurately predict the structure of water near the surface. To accurately capture surface effects on the water structure, we add a coarse-grained correction potential between wall atoms and water coarse-grained beads. We use an empirical potential-based quasi-continuum theory (EQT) (J. Chem. Phys.2007, 127, 174701) to derive and evaluate optimal parameters for the coarse-grained potential model. We evaluate the ability of our model to predict the structure of confined water for two different types of surfaces-a silicon slit channel and a graphite slit channel-and show that the results predicted by EQT are in good agreement with all-atom molecular dynamics results across multiple length scales. We also demonstrate that the coarse-grained potential parameters optimized using EQT work well even in the coarse-grained molecular dynamics simulations.