Electronic structure of coinage metal clusters M20 (M = Cu, Ag, Au) from density functional calculations and the phenomenological shell model

Abstract

The first-principles calculations are carried out to explore more intensely on geometric, spectroscopic and electronic properties of M20 (M = Cu, Ag, Au) species. Computed results show that the global minima of these clusters are compact, nearly spherical structures, while other low-lying isomers exhibit the oblate or probate shapes. For Cu20, we find it is in a C3 symmetry form rather than the Cs conformation as previously suggested. The vertical ionization energies for lower-lying isomers are also computed and assigned with respect to available experimental values. Although several isomers were predicted to be similar in energy content, the corresponding vibrational signatures are so distinctive that could be used as fingerprint signals to identify their geometrical forms. More importantly, the enhanced stability of these systems can be understood in terms of the phenomenological shell model. Computed results also recognize that the structures and properties of Ag20 and Cu20 clusters are similar and prefer compact structures, while Au20 cluster exhibits structures different from with a tetrahedral form.