Theoretical Investigation of the H3O+(H2O)4 Cluster

The low-lying minima on the Born−Oppenheimer potential energy surface of the H 3 O + (H 2 O) 4 cluster are investigated by effective valence bond (EVB), density functional, and MP2 methods. Although Becke3LYP and MP2 calculations predict the same global minimum structure, the relative energies of various structures obtained by these two approaches differ by up to 1.7 kcal/mol. Even larger differences are found between the relative energies calculated at the EVB and MP2 levels of theory. Vibrational spectra are calculated for each of the minimum energy species.