Enumeration of Topology-Distinct Structures and Possible Stable Structures of Protonated Water Clusters, H3O+(H2O)n−1 (n≤5)

Abstract

Abstract A rooted digraph is regarded as a protonated water (PW) cluster, and a hydrogen bond (H-B) matrix can represent a rooted digraph. All possible topology-distinct patterns corresponding to PW clusters containing up to 8 water molecules were enumerated by using H-B matrices. From close investigation of the structural patterns obtained, we found several restrictions that should be satisfied for a structure of the PW clusters to be stable. The generated H-B matrices of the restrictive rooted digraph were used as the theoretical framework to obtain all the topology-distinct local minima of H3O+(H2O)n−1 (n≤5), at the level of MP2/6-31G∗∗ of ab initio MO method. For PW clusters up to tetramers, the local minimum structures that we generated are same as those in the literatures. For PW pentamers, we found some new local minimum structures, which had not been obtained previously.