Theoretical Study of Small Scandium-Doped Silver Clusters ScAg_n with n = 1-7: σ-Aromatic Feature

Geometry, chemical bonding, and aromatic feature of a series of small silver clusters doped by an Sc atom (ScAg_n with n = 1-7) were investigated by means of density functional theory calculations. A planar shape is found for ScAg_n including n from 4 to 7. The growth mechanism is established for the formation of the hexagonal and heptagonal metallic cycles following increase of the number of Ag atoms. Particularly, both clusters ScAg₆^- and ScAg₇ present a planar cyclic form in which the Sc atom is situated at the central position of the Ag₆ and Ag₇ cycles. The σ aromaticity is unambiguously demonstrated by the existence of strongly diatropic current flows within the ring in both ScAg₆^- and ScAg₇. The isovalent ScCu₇ cluster has a similar ring current characteristic. In the Sc-doped ScAg_n clusters, a delocalized bonding pattern is found as a connector between the dopant Sc and the Ag_n host, as indicated by an ELI_D analysis.