Chemical Bonding and Electronic Structure of Small Homonuclear Clusters of Elements of Groups IA, IIA, IIIA and IVA

Term rules for simple metal clusters

Hund’s term rules are only valid for isolated atoms, but have no generalization for molecules or clusters of several atoms. We present a benchmark calculation of Al₂ and Al₃, for which we find the high and low-spin ground states ³Π_u and , respectively. We show that the relative stabilities of all the molecular terms of Al₂ and Al₃ can be described by simple rules pertaining to bonding structures and symmetries, which serve as guiding principles to determine ground state terms of arbitrary multi-atom clusters.