Empirical models for the hydration of protons

Two empirical models are considered for the hydrates H+(H2O)n. In one, a rigid hydronium unit interacts with n−1 water molecules, and in another, a single proton with an effective hard-core radius interacts with n waters. In each case, the polarizable representation of the water molecule developed by Kozack and Jordan is used. The two models are employed in a study of clusters with 1≤n≤7 and it is found that while both yield minimum-energy structures in good agreement with ab initio studies, the experimental hydration energies are much better accounted for within the proton model.