PHASE-EQUILIBRIA IN EXTENDED SIMPLE POINT-CHARGE ICE-WATER SYSTEMS

The characteristics of the solid/liquid transition for a modified Simp le Point Charge model of water have been determined using free energy calculations supported by nonequilibrium Molecular Dynamics (NEMD) sim ulations. We have considered the behavior of liquid water and of a var iety of ice phases. Unlike real water, the stable crystalline phase at 1 bar is not hexagonal ice I, but a denser new ice phase. The melting point of this ice was found to be near 295 K. The lower-density ices, I-h and I-c, are less stable than water down to the glass transition temperature. The conclusions are supported by NEMD simulations of the behavior of the planar crystal-liquid interface for these different ca ses. The first report of the growth of ice from water using molecular simulation is shown here. The influence of the components of the inter molecular potential on the stability of the ice polymorphs is investig ated. It is found that, for ice I to be the stable phase, the Lennard- Jones attractive part should be reduced, and the potential switching f unction should be used at longer distances. Properties of the supercoo led liquid water are also presented. (C) 1995 American Institute of Ph ysics.