We propose a general framework to construct explicit water models based on the concept of optimal point charge approximation. The central idea is to distribute the point charges to best reproduce the lowest order multipole moments of the water molecule. We describe the construction and performance of a new non-polarizable, 4-point, 3-charge rigid water model, called OPC. The optimal values for the dipole � and the square quadtupole moment QT are determined as best fit values that reproduce key experimental properties of water in liquid phase. The low dimensionality of the parameter space �-Q?T permits a virtually exhaustive search. The remaining key moments are fixed to values obtained from high quality QM calculations. The OPC is shown to yield the correct values for the self-diffusion coefficient, the dielectric constant, the density and the first peak position in the radial distribution function essentially within experimental uncertainties. A remarkable accuracy is also obtained for the heat of vaporization and isobaric heat capacity. The agreement holds for a wide range of temperatures. The general insight into the building of simplified water models is discussed. The OPC water model is included in the solvent library of the Amber molecular dynamics (MD) software package. Preliminary all-atom MD simulation results demonstrate promise of the new model.

Optimal point charge water model

248th National Meeting (2014)

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