Carbon dimer in silicon cage: A class of highly stable silicon carbide clusters

Abstract

A class of silicon carbide cage clusters with two carbon atoms inside the silicon cage and with high stabilities are presented. The theoretical formalism used is Hartree-Fock theory followed by second-order many-body perturbation theory to account for correlation effects, and geometry optimizations at the second-order perturbation theory level are performed without any symmetry constraints. The smallest ``cage'' is found to be a silicon cube with the carbon dimer inside the cube. Based on the simultaneous criteria of high binding energy, high vertical ionization potential, high [highest occupied--lowest unoccupied molecular orbital (HOMO-LUMO)] gap, and a low vertical electron affinity, ${\mathrm{Si}}_{14}{\mathrm{C}}_{2},$ with a close fullerenelike structure, is predicted to be a particularly stable cluster both at the all-electron and at the pseudopotential level of calculations. The $\mathrm{C}---\mathrm{C}$ bond lengths and the HOMO-LUMO gaps of the clusters are both found to oscillate with cluster size.