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 statistical mechanical Monte Carlo bath of 89 water molecules was determined using 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 bond length increase is in good agreement with recent neutron diffraction results; liquid water is closer in bond length to gas phase water than ice. In combination with the optimized angle HOH bond angle approaching tetrahedral, the conclusion is that quadrupole moment dominates the water geometry in the liquid phase. (C) 1997 American Institute of Physics.