Geometric, energetic, and bonding properties of neutral and charged copper-doped silicon clusters

The geometric, energetic, and bonding properties of CuSin (n=4, 6, 8, 10, and 12) clusters in neutral and charged states are studied systematically using a hybrid density functional method (B3LYP). The Si-n frameworks in most isomers of CuSin are found to adopt the geometries of the ground-state or low-lying isomers of Si-n or Sin+1, with Cu at various substitutional or adsorption sites. Several cagelike structures with Cu at the center site are found for CuSi10 and CuSi12. A hexagonal double-chair structure with Cu at the center, which bears a similarity to the structure of a regular hexagonal prism recently reported for WSi12+ [H. Hiura , Phys. Rev. Lett. 86, 1733 (2001)], is identified as the best candidate for the ground state of CuSi12. The Cu-Si bond in CuSin is strong for the substitutional and the center-site structures, but weak for the adsorption structures where charge transfer and resulting ionic interaction is found to play a more important role. The Cu atom reveals a similar bonding character to the replaced Si atom in the substitutional structures except for CuSi12, where the Cu atom both in the substitutional and in the center-site structures is found to form multicenter bonds with as many as nine (substitutional) to 12 (center-site) Si atoms. Various energetic properties, including binding and dissociation energies, ionization potentials, electron affinities, and vertical detachment energies are reported for CuSin.