Theoretical Studies of Transition-Metal-Doped Single-Walled Carbon Nanotubes

We have studied single-walled carbon nanotubes (SWCNTs) doped with transition metal (TM) atoms with both exo and endo doping configurations. The electronic and geometric properties of these TM-doped SWCNTs were calculated within density functional theory. It was found that the endo-doped SWCNTs are less stable than the exo-doped counterparts due to the large geometric strain of the deformation in the endo-doped nanotubes. On the basis of partial charge analysis, the TM-doped SWCNTs have localized net charge distributions, whereas the spin densities in Sc-, Co-, and Cu-doped SWCNTs are delocalized over the entire nanotubes. The TM-doped SWCNTs are mostly metallic or narrow-gap semiconductive. With highly localized frontier molecular orbitals, the exo-doped SWCNTs are better electron donors than the corresponding endo-doped systems. As the dopant TM changes from Sc to Zn in the same row of the periodic table or from the top to the bottom in the same Pt group, the energy of the highest occupied crystal orbital of the TM-doped SWCNTs decreases, indicating a reduced electron donating ability.