Stable geometric and electronic structures of gold-coated nanoparticles M@Au12 (M=5d transition metals, from Hf to Hg):: Ih or Oh?

The geometric and electronic structures of 5d transition metal "impurities" Hf to Hg encapsulated in icosahedral and cuboctahedral Au-12 cages have been investigated theoretically. The best density functional results of the small molecules Au-12, AuH, AuCl, and AuCu were obtained for the geometric structures with X alpha, and for the electronic energies of those frozen structures with VBP. The same procedure was then applied to the clusters. At the zeroth order regular relativistic approximation ZORA, both at the spin-averaged scalar and at the spin - orbit-split spinor levels, the cuboctahedral clusters tend to be more stable than their icosahedral isomers, except for W@Au-12. The neutral clusters have electronic closed shells only for I-h and O-h W@Au-12 and for O-h Hg@Au-12. The embedding energy of M into Au-12 is less attractive for the later transition metal atoms M.