Monte Carlo simulations of water-ice layers on a model silver iodide substrate: A comparison with bulk ice systems.

Abstract

Two water layers adsorbed on a model silver iodide basal face are simulated at nine temperatures from 150 to 425 K using Monte Carlo methods. The periodic unit cell of 96 internally rigid water molecules (interacting via the revised central-force potentials) couples to the rigid-substrate atoms via effective pair potentials with Lennard-Jones short-range and Coulomb long-range terms. The distribution of molecules perpendicular to the substrate exhibits layering, and individual layer structure factors, dipole moments, and ``pseudodiffusion'' coefficients are calculated. A complex temperature dependence with the two layers taking on different solidlike, quasiliquid, or liquid properties at the same T is observed. Both layers appear to be solid at the lowest T studied. But for T\ensuremath{\ge}265 K the upper layer becomes increasingly liquidlike with increasing T, whereas the lower layer of water molecules remains generally solidlike up to T=325 K. Comparisons are made with constant number, volume, and temperature bulk ice Monte Carlo simulations and (flexible molecule) molecular-dynamics simulations using the same water-water potentials. Pseudodiffusion coefficients are compared with experimental values for ice, water, and with a quasiliquidlike layer of water on ice.