Electronic shell effects in triaxially deformed metal clusters: A systematic interpretation of experimental observations

Abstract

We develop and apply a semiempirical shell-correction method to calculate the binding energies of open-shell, neutral and charged, simple-metal clusters, which can be modeled as triaxially deformed jellium droplets. Systematics of ground-state properties of clusters with sizes up to 100 atoms, such as ionization potentials and electron affinities, are studied and compared to available experimental measurements on sodium, potassium, and copper clusters. We also report on systematics of the energetics of fission channels for doubly charged cationic and anionic species, as well as the energetics of monomer and dimer separation channels, and compare them to experimental data. Pertaining to characteristic patterns as a function of cluster size in the above quantities, triaxial shell effects exhibit a rich structure, yielding overall substantial improvement in the agreement between theory and experiment. In particular, we show that the lifting of the degeneracies in the electron spectra via cluster triaxial-shape deformations underlies the appearance of odd-even alternations in such patterns. Furthermore, our analysis of ground-state properties can lead to unambiguous assignments of equilibrium cluster shapes, as well as shape isomers.