On the existence of very large nonadditivities for clusters of distorted water molecules

Abstract

We present a detailed analysis, both at the self-consistent field and electronic correlation levels, of the many-body expansion of water clusters occurring with intramolecular relaxation. The results show extremely large nonadditivities, which lead to the proposal of an alternative many-body expansion that shows convergence. From the results, it is clear that there is substantial intra–intermolecular coupling, an important contribution of the correlation energy to the stability of these clusters, and a crucial role of cooperativity in the stability of the condensed phases of water. It is also clear that these refinements should be included in water models attempting to simulate this substance.