Clusterization of water molecules on crystalline β-AgI surface. Computer experiment

The free energy and the work of formation of the clusters of water molecules from the vapor on the ideal continuous crystalline surface of silver iodide at 260 and 300 K are calculated with the Monte Carlo method for a bicanonical statistical ensemble. Long-range electrostatic and polarization interactions with the surface are calculated with the two-dimensional Ewald method. It is shown that the adsorption of water molecules is accompanied by their intense clusterization. At negative Celsius temperatures, hydrogen-bonded molecules form the chains on the crystal surface. The closure of chains into rings begins with the clusters containing five molecules. As cluster sizes increase, the competition between five-and six-membered cycles is ended in favor of six-membered cycles. The substrate field stimulates the formation of six-membered cycles. Entropic effects strongly level the influence of clusterization on the probability of adsorption. Within the size interval 1 < N < 15, there are two clusterization barriers whose heights are negligible and equal to about 2k _B T. The presence of a substrate lowers the vapor pressure of clusterization by more than an order of magnitude.