Recently, there have been extensive studies on the coarse-grained (CG) modeling of water to understand its anomalous properties. To faithfully reproduce the strong local correlations in liquid water, an explicit higher-order interaction is essential. However, the advantage of CG is then offset by the large computational cost for parameterization and simulation. In this work, we propose an alternative statistical mechanical approach for constructing a bottom-up CG water model using only pairwise interactions that, unlike other models, projects many-body interactions onto pairwise basis sets. A new CG water model named the Bottom-Up Many-body Projected Water (BUMPer) is presented with parameterization from different atomistic water force fields: SPC/E, SPC/Fw, TIP4P/2005, and TIP4P/Ice. The robustness of the BUMPer models is demonstrated by calculating pair and N-body correlation functions. The implicitly embedded three-body interaction of the BUMPer model can be further witnessed by the crystallization behavior at the liquid-ice interface. The real advantage of the BUMPer model is in its thermodynamic representability of entropy and free energy: it can qualitatively capture the missing entropy during coarse-graining, while most other CG water models yield unphysical entropy values (i.e., opposite signs). The BUMPer model gives an accurate representation of thermodynamics and is designed to be transferable to different temperatures from 280 K to 360 K. This BUMPer model represents an extensive improvement over existing bottom-up CG water models by both extending the accuracy and applicability of CG water models in a more rigorous framework while reducing computational cost.

New coarse-grained model for water with improved thermodynamic and structural properties: Bottom-up many-body projected water (BUMPer)

2019 Fall National Meeting

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