Atomic and electronic shells of Al-77

We have carried out a first-principles calculation on the atomic and electr onic shell structures for the experimentally characterized Al-77 The onionl ike Al-77 structure can be described by a stable Al-13 inner core covered b y a two-layer atomic shell. The stability of Al-77 is confirmed by structur al optimization and electronic structure calculations. The interaction betw een Al-77 and its ligands is found to be ionic like. Our results on the ele ctronic structure provide important information on electronic shell structu res in large Al clusters.