SELECTION OF CONFIGURATIONS FOR PARAMETERIZATION OF 2-BODY INTERACTION POTENTIALS

Ab initio molecular orbital calculations at the RHF/6-31+G* and MP2/6-31+G* levels have been performed on three sets of water dimers, each comprising approximately 700 different configurations, selected from complete sets of configurations present in samples of water equilibrated at 25, 75, and 500°C, respectively, using standard molecular dynamics techniques. Each of these data sets has been used to parameterize intermolecular potential energy functions comprising van der Waals terms to account for steric interactions and point-multipole interactions to account for electrostatic effects. Fits to 25 and 75°C data are of comparable quality and are significantly better than fits to the corresponding 500°C data or to data corresponding to water configurations chosen from a random-walk procedure. These findings suggest that repulsive configurations, which are more prevalent in the 500°C and random-walk data sets, are not fit as well as more tightly bound configurations by the simple functional form used here. © 1990 American Chemical Society.