Molecular Orbital Calculations of Water-Ice Surface Interactions

Abstract

Abstract Detailed knowledge of the energetics of the interaction of a water monomer with an ice surface is important in understanding the factors which control both the nucleation and the growth of ice. In this work we model this interaction by using a small section of an ice surface and semi-empirical quantum-mechanical calculations of the CNDO/INDO type to investigate the energetics of a gas-phase molecule approaching the surface. In the attempt to simplify the system as much as possible while retaining the essential features of the "real" physical situation, 13 water molecules arranged in the lattice positions for ice Ih were used to represent the surface. Electron-density plots for both basal and prism surfaces were generated. Potential-energy curves were calculated for a monomer approaching a number of different sites on each type of surface. Monomer-surface binding energies varied from approximately 17 to 33 kJ/mol for the surface sites examined. Ion pairs of the H30 +-OH- type were included in the surface and their effect on the energy of interaction with an incoming monomer calculated. For these studies no distortion of the ice surface was allowed. The energies found follow the same trends as observed for a free monomer-ion interaction.