The geometrical and electronic structures of 5d transition metal (TM) impurities encapsulated in the icosahedral and cuboctahedral Ag12 cages have been investigated systematically by a relativistic density functional theory method. Calculated results show that the M—Ag bond lengths depend on two factors: the sum of atomic radii and the cluster’s electronic structure. The binding energy of M@Ag12 varies with the embedding energy of M into Ag12 cage and with the distortion energy of the originally empty Ag12 cage upon embedding the M atom. The clusters with bonding HOMO are more stable than those with anti-bonding HOMO. It was found that the icosahedral clusters were not always more stable than their cuboctahedral isomers, while the cuboctahedral clusters of Hf@Ag12, Ir@Ag12, Au@Ag12 and Hg@Ag12 were more stable than their icosahedral isomers.

Key words: density functional theory, M@Ag12 cluster, Ih, Oh