HYDRATION OF SODIUM IN WATER CLUSTERS

Hydration of sodium in water clusters, Na(H2O)n, 1 less-than-or-equal-to n less-than-or-equal-to 8, is investigated using nonlocal pseudopotentials and local-spin-density functional theory, with exchange-correlation gradient corrections. Addition of water molecules to an Na atom results in a successive decrease in the ionization potential, with a marked reduced variation for n > 4. This reflects the formation of a molecular shell about the Na for n is similar to 4, accompanied by expulsion of the metal valence electron from the hydration cavity and its delocalization in a ''surface Rydberg-like state.''