Doping the armchair single-walled carbon nanotubes by silicon substitutions: A density functional theory study

In this paper the nanotubes obtained by silicon atoms substitutionally doping the armchair single-walled carbon nanotubes were investigated by quantum chemistry calculations under the framework of density functional theory. The geometrical structures, relative stabilities and electronic properties of the fifteen Si-doped tubes were studied in details and compared with those of the pristine (5, 5) tubes. It is found that the Si atoms tend to “pop out” from the original positions when the silicon atoms are introduced into the nanotubes. The Si-doped nanotubes exhibit lower thermodynamic stability than those of the undoped tubes from viewpoint of cohesive energy, and this is similar to the case of the silicon doped zigzag nanotubes. The energy levels of the frontier orbitals vary very little when the silicon atom is introduced into the nanotubes. However, most hybrid nanotubes present smaller energy gaps than those of the pristine ones.