Interaction of Aluminum(III) with water. An ab initio study

Hydrated Al3+ ions [Al(H2O)n]3+, n=1–6, were examined with ab initio self-consistent field (SCF) calculations. The relative contributions of two-, three-, and higher-body terms to the total interaction energy for an [Al(H2O)6]3+ complex were calculated. The sum of all three-body contributions amounts to ∼30% of the sum of all pair-additive contributions and is opposite in sign. The three-body energy contributions were also derived for two types of [Al(H2O)2]3+ complexes. In the first type, both water molecules reside in the first hydration shell of Al3+ and in the second type there is one in the first shell and one in the second. Altogether 15,500 triplets were investigated and analytical two- and three-body potential energy functions were derived via a fitting procedure.