PNNL

Abstract

In this work we examine the consequences of incorporating the ab-initio derived monomer potential energy surface and non-linear dipole surface of Partridge and Schwenke [J. Chem. Phys. 106, 4618 (1997)] into the previously developed TTM2-R model of Burnham et al. [J. Chem. Phys. xx. yyyy (2001)] in order to develop a new, all-atom polarizable, flexible model for water (TTM2-F). We found that the use of the non-linear 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 reproduces the n=2-6 cluster binding energies to within an RMS deviation of 0.05 kcal/mol per hydrogen bond with respect to the MP2 complete basis set estimates.