Theoretical study of carbon doped small silicon clusters: Electron affinities of Si_nC (n=2-5)

The geometries and energies of Si_nC and Si_nC^- (n=2-5) were investigated with ab initio MO calculations including electron correlation. The Møller-Plesset perturbation theory was used for n=3-5. The configuration interaction (CI) calculations were carried out for n=2 and 3. The most stable isomers of the neutral Si_nC clusters have the structure in which an Si atom having the largest sp hybridization in the corresponding Si_n+1 cluster is replaced by a C atom. For their anions, the structures in which an excess electron is distributed avoiding a C atom become stable. Moreover, the adiabatic electron affinities of Si_nC and vertical detachment energies of anionic Si_nC^- were computed. They reproduced the trends of photoelectron spectra of Si_nC^- reported previously.