Development of transferable interaction models for water. IV.A flexible, all-atom polarizable potential (TTM2-F) based on geometry depencent charges derived from an ab initio monomer dipole moment surface

摘要

In this work we examine the consequences of incroporating the ab initio derived monomer potential-energy surfce and nonlinear dipole surface of Partridge and Schwenke [J. Chem. Phys. 106, 4618 (1997)] into th previously developed TTM2-R model of Burnham et al. [J. Chem. Phys. 116, 1500 (2002)] in order to develop a new, all-atom polarizable, flexible model for water (TTM2-F) We found that the use of the nonlinear dipole surface is essential in modeling the change in the internal geometry of interacting water molecules and, in particular, the increase in the internal H-O-H bend angle with cluster size. This is the first demonstration of a flexible model which shows an increase in the bending angle in clusters. An explanation for this behavior is presented using the concept of geometric polarizabilities. The model furthermore reporduces the n=2-6 cluster binding energies to within an RMS deviation of 0.05 kcal/mol per hydrogne bond with respect to the MP2 compelte basis set estimates. Preliminary results for the liquid with the new model are also presented.