Monte Carlo studies of water monolayer clusters on substrates: Hexagonal AgI

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Abstract
A Monte Carlo procedure is used to study the stability and structure of small water clusters adsorbed on model basal and prism faces of hexagonal AgI. Effective pair potentials for the H2O–AgI interaction [B. N. Hale and J. Kiefer, J. Chem. Phys. 73, 923 (1980)] and the revised central force potentials for the H2O–H2O interaction [F. H. Stillinger and A. Rahman, J. Chem. Phys. 68, 666 (1978)] are used to determine average internal cluster binding energy and average cluster–substrate binding energy for water clusters containing 6, 24, and 44 water molecules at temperatures 240, 265, and 298 K. The results (using an effective substrate point charge of 0.4e) give between 5 and 6 kcal/mol per molecule for each of the above average binding energies. The iodine exposed basal AgI face organizes the H2O into five- and six-membered rings centered around the exposed I atoms. The prism face appears less effective in promoting ring structure and gives, in general, lower average internal cluster binding energies. The basal AgI face positions the water molecules (in H2O–substrate high binding sites) about 2.8 A apart while the water–water interactions orient the H2O dipole moments into configurations favorable for hydrogen bonding. The resulting six-membered ring structure is similar to that in ice Ih (crinkled) basal face layers, and appears to be qualitatively the same for all the temperatures studied.