A high level ab initio method and an ABEEM/MM model had been applied to study the hydronium ion clusters H3O＋(H2O)n (n＝1～6). The low energy geometries had been optimized and the binding energy and the stability had been discussed, revealing the preponderant existence of the local structure of the H3O＋(H2O)3 cluster. The charge distribution of H3O＋(H2O)6VIa has also been analyzed, indicating that the strength of H-bonds of the first solvation shell with the hydronium ion is stronger than that with the second solvation shell. The results of the ABEEM/MM model are well coincident with those from ab initio method.

Key words: hydronium ion cluster, ab initio method, ABEEM/MM model