CLUSTER AND SUPERCELL CALCULATIONS FOR CARBON-DOPED SILICON

The substitution of carbon in bulk silicon is investigated at the Hart ree-Fock level using a cluster model, and the results compared directl y with periodic 'supercell' calculations based on the same Hamiltonian , basis set and computational scheme. To study variations in calculate d properties with cluster size, hydrogen-saturated clusters containing five, thirty-five and eighty-seven Si atoms are considered, with rela xation of up to the second shell of neighbours surrounding carbon impu rities. The calculated atomic relaxations and charge distributions in supercells and large clusters are reasonably similar. In relaxed clust ers however, boundary effects lead to appreciable differences in calcu lated defect formation energies.