Structure and energetics of small water clusters

Abstract

A study of small water clusters composed of two to seven molecules has been performed by using the revised empirical potential function (REPF). Cluster structures corresponding to the minima of potential energy have been characterized structurally and energetically. In general, cyclic structures are energetically more favorable than open ones as to the clusters containing three to six molecules. It is found that a unique structure for the large clusters is meaningless, but what is physically relevant is the statistical distribution of different configurations of clusters, since the various configurations of each cluster have nearly the same value in energy. From the comparison of the total interaction energy per molecule of each cluster, cyclic pentamer is found to be as a most favorable configuration. Cyclic tetramer has a puckered form, and cyclic heptamer is highly puckered and has only three hydrogen bonds. As the increase of cluster sizes, the more favorable cluster forms are cyclic structures. We note, here, that if clusters exist in liquid water, an infinite long chain may not exist and the major are probably cyclic pentamers.