GEOMETRY OPTIMIZATION OF A WATER MOLECULE IN WATER - A COMBINED QUANTUM-CHEMICAL AND STATISTICAL-MECHANICAL TREATMENT

A Hartree-Fock optimized geometry for a water molecule in a statistica l mechanical Monte Carlo bath of 89 water molecules was determined usi ng a polarization model. Both the O-H bond lengths and angle HOH bond angle were found to increase from the gas to the liquid phase. The bon d length increase is in good agreement with recent neutron diffraction results; liquid water is closer in bond length to gas phase water tha n ice. In combination with the optimized angle HOH bond angle approach ing tetrahedral, the conclusion is that quadrupole moment dominates th e water geometry in the liquid phase. (C) 1997 American Institute of P hysics.