Analytic potential for water: a Monte Carlo study

We have recently studied by Monte Carlo computer simulation a potential function for liquid water that is tractable analytically. This potential is a modification of the BBL potential with an additional octopolar interaction term. This potential consisted of a hard core plus electrostatic and short range orientational terms. In the present study we introduce a modification in which the repulsive spherical core is softened by means of an exponential term. The atom-atom pair correlation functions for oxygen-oxygen, oxygen-hydrogen and hydrogen-hydrogen obtained for this new potential are in excellent agreement with the neutron scattering experiments. The simulations indicate a possible percolation transition for the hydrogen bonds, such as the one proposed by Stanley and collaborators some time ago, since small changes in the potential seem to lock in or lock out the characteristic water structure.