A multistate empirical valence bond approach to a polarizable and flexiblewater model

A new polarizable and flexible water potential has been developed based on the multistate empirical valence bond (MS-EVB) method. The model adds a cha rge-determination step to the simple point charge/flexible (SPC/F) potentia l. Two models have been developed: one that is polarizable only along the p rincipal axis, and another that is polarizable in both directions within th e molecular plane. The two models give nearly identical radial distribution functions (RDF) for the three site-site RDFs in water: oxygen-oxygen, oxyg en-hydrogen, and hydrogen-hydrogen. The new model exhibits a liquid structu re that is more ordered than SPC/F but is still well matched to experiment. The gas-phase monomer and dimer properties of the polarizable models are m uch closer to the experimental result than is SPC/F. Experimental condensed phase properties, such as the bond angle, bond length, molecular dipole mo ment, and total energy, are also reasonably well reproduced. The static die lectric constant and self-diffusion constant of the model with two directio ns of polarizability are also reasonably accurate. The MS-EVB method is sho wn to provide a simple approach to including both polarizability and bond f lexibility into a water potential.