Carbon Dimer in Silicon Cage: A Class of Highly Stable Silicon Carbide Clusters

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 homo-lumo gap, and low electron affinity, Si_14C_2 with a close fullerene like structure, is predicted to be a particularly stable cluster both al all-electron and at pseudopotential level of calculations. The C-C bond lengths and the HOMO-LUMO gaps of the clusters are both found to oscillate with the cluster size.