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

Abstract

The geometric, energetic, and bonding properties of ${\mathrm{CuSi}}_{n}$ ($n=4,$ 6, 8, 10, and 12) clusters in neutral and charged states are studied systematically using a hybrid density functional method (B3LYP). The ${\mathrm{Si}}_{n}$ frameworks in most isomers of ${\mathrm{CuSi}}_{n}$ are found to adopt the geometries of the ground-state or low-lying isomers of ${\mathrm{Si}}_{n}$ or ${\mathrm{Si}}_{n+1},$ with Cu at various substitutional or adsorption sites. Several cagelike structures with Cu at the center site are found for ${\mathrm{CuSi}}_{10}$ and ${\mathrm{CuSi}}_{12}.$ 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 ${\mathrm{WSi}}_{12}^{+}$ [H. Hiura et al., Phys. Rev. Lett. 86, 1733 (2001)], is identified as the best candidate for the ground state of ${\mathrm{CuSi}}_{12}.$ The Cu-Si bond in ${\mathrm{CuSi}}_{n}$ 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 ${\mathrm{CuSi}}_{12},$ 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 ${\mathrm{CuSi}}_{n}.$