First-principles investigation on B/N co-doping of ultra small diameter metallic single-walled carbon nanotubes

- Small energy gaps exists in both (3,3) and (5,0) tubes after B/N co-doping.
- In most case the energy gaps increase with increasing the symmetry destruction factor δ.
- The electronic structures of B/N co-doped SWCNTs with B- or N-rich impurities are converted into metal from semiconductor.