Theoretical studies of the interaction of H₂O with small clusters of beryllium atoms^†

The interaction of a water molecule with a cluster of beryllium atoms [Be_n … OH₂, n = 1–5] has been examined by ab initio molecular orbital methods. The dependence of interaction energy and structure on the size of the cluster was investigated with a large basis set including polarization functions. The effects of electron correlation were considered by Møller-Plesset perturbation theory. A surprisingly large increase in the interaction energy from 5 kcal/mol to 23 kcal/mol occurs when the cluster size reaches three atoms with a decrease in the Be-O distance from 1.71 to 1.64 Å. The dissociation energy shows no further large changes when the cluster size is increased to four and five atoms. The H₂O is found to prefer corner binding sites significantly over edge or face sites on the clusters. The nature of the bonding between H₂O and the Be clusters is discussed.