THE INDUCED POLARIZATION OF THE WATER MOLECULE

The molecular polarization potential map (MPP) of the water molecule computed at the SCF level with a double zeta basis set with two sets of polarization functions was used as reference to assess the accuracy of the induced polarization description of various force fields. The MPP was computed on grids of points defined on shells ranging from 1.0 to 4.0 times the van der Waals radius. The comparison between the reference MPP and the one computed with different parameterizations shows large average deviations for some of them, while others exhibit similar behaviour to that of the ab initio map. The MPP has been used to derive atom polarizabilities by a least-squares fitting. Two proposed sets of parameters were developed. First, using all the points calculated, the procedure yields 0.911 angstrom for a single polarizability centered on the oxygen atom and 0.702 and 0.106 angstrom3 for a two-parameter fit centered on the oxygen and hydrogens, respectively. Second, if only layers between 1.2 and 4.0 times the van der Waals radius are considered, the one-parameter fit yields a polarizability of 1.041 angstrom3, whereas the two-parameter fit yields 0.817 and 0.112 angstrom3 for the oxygen and hydrogen.