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 Al(2) and Al(3), for which we find the high and low-spin ground states (3)Π(u) and [Image: see text], respectively. We show that the relative stabilities of all the molecular terms of Al(2) and Al(3) 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.