A WATER-WATER POTENTIAL DERIVED USING A QUANTUM MONTE-CARLO VIBRATIONAL ANALYSIS

A difficulty in the generation and testing of intermolecular interacti on potentials has to do with the effects of vibrational motion. For we ak modes, the vibrational excursions can be and often are sizable. So, not only do model potentials have to be suitable over a considerable range, they must also be accurate with respect to experimental data th at reflects the vibrational averaging (i.e., on-average structures). I n this report, we present an explicit interaction potential for the wa ter dimer that has been devised with a systematic treatment of vibrati onal effects by means of quantum Monte Carlo treatment of the vibratio nal ground state. The model potential uses intrinsic electrical proper ties of isolated water and four empirical parameters. An iterative pro cedure based on matching measured on-average rotational constants to c alculated values was used to select the atom-atom Lennard-Jones (empir ical) parameters. We present the results of these calculations, includ ing zero point vibrational energies and on-average separations.