The hybrid nanostructures made of single-walled carbon nanotubes substitutionally doped with silicon atoms were investigated by quantum chemistry calculations based on density functional theory in this paper. The zigzag (12, 0) tube was considered to construct the Si-doped tubes. The geometrical structures, relative stabilities and electronic properties of the doped tubes were studied in details and compared with those of the pristine nanotubes. It is found that the Si-doped nanotubes exhibit lower thermodynamic stability than those of the undoped tubes from viewpoint of cohesive energy. The energy levels of the frontier orbitals vary very little when the silicon atom is introduced into the nanotubes. However, most doped tubes present larger Eg than those of the pristine ones.
