Global minima and energetics of Li +(H 2O) n and Ca 2+(H 2O) n clusters for n ⩽ 20

Abstract

We present candidate structures for the global potential energy minima of X(H 2O) n (X = Li +, Ca 2+) clusters with n ⩽ 20. The TIP4P rigid body water–water potential is employed, together with cation–water interactions that are represented as a sum of Coulomb and Lennard–Jones terms. We find that in the Li + global minima the cation tends to be located on the cluster surface with a preferred coordination number of four water molecules in tetrahedral positions. In contrast, for Ca 2+ clusters the cation occupies an interior site surrounded by eight water molecules in a square anti-prismatic arrangement.