ON THE IMPLEMENTATION OF FRIEDMAN BOUNDARY-CONDITIONS IN LIQUID WATERSIMULATIONS

We have applied the image approximation to the reaction field as sugge sted by H.L. Friedman [Mol. Phys., 29, 1533 (1975)] by investigating a ppropriate cavity sizes and system parameters for use in molecular sim ulations. The energy of and the structure around a central simple poin t charge (SPC) water molecule in a dielectric cavity was found to be i n good agreement with the properties of a liquid sample. To confine th e water molecules within the cavity, we introduced a short-range repul sion between a real charge and its image as the Lennard-Jones repulsiv e potential between oxygen atoms of the SPC potential. For a system of 65 water molecules a cavity radius of 10.45 angstrom is appropriate; this radius is altered to 12.00 angstrom for a cavity surrounding 113 molecules. The effect of the boundary is restricted to the outermost w ater layer which is in contact with the dielectric continuum.