A theoretical study of nonadditive effects in four water tetramers

Abstract

The properties of four water tetramers have been investigated using ab initio computations at the MP2/6-311+G(2d,2p) level. The four tetramers correspond to various molecular arrangements. The computations showed that, with respect to the water dimer, a significant reinforcement of the hydrogen bonds occurs due to cooperative effects when water molecules adopt a pattern where they are simultaneously donor and acceptor of a hydrogen bond. This is consistent with an interpretation of hydrogen bonding in terms of charge-transfer phenomena in the hydrogen bond region and suggests that the origin of a part of the cooperativity occurring in water aggregates arises from cooperative charge-transfer phenomena. Analysis of the intermolecular interaction energies, carried out by both the ab initio supermolecule approach and the SIBFA molecular mechanics procedure, showed the inductive effects to be mainly responsible for the tetramer nonadditive effect.