STRUCTURE OF H+(H2O)N CLUSTERS NEAR THE MAGIC NUMBER N=21

A model potential for proton hydrates, in which the system is treated as a collection of rigid water monomers plus a lone proton, is used to investigate H+ (H2O)n Clusters for n near the magic number of 21. Various configurations which are local minima in the total energy are generated. Both clathrate-like and amorphous structures are examined. In all cases, the hydronium-like unit is four coordinated, donating hydrogen bonds to three water molecules and interacting with the fourth through a favorable charge-dipole interaction. Both hydrogen bonding and ion-dipole interactions play a role in determining the stability of a given configuration. These features make the cluster energies sensitive to the input potentials.