Nitrogen doping and chirality of carbon nanotubes

We have theoretically studied nitrogen doping of carbon nanotubes in a periodic supercell using density functional theory. We find that the most stable isomer is different for different chiralities of the tube. In the (10,0) tube, N atoms tend to be uniformly distributed, while they prefer to be adjacent to each other in (5,5) tube. As more nitrogen atoms are introduced in (5,5) tube, they are aligned parallel to the tube axis in two rows, breaking the N-N single bonds and forming aromatic (4n+2)π systems. This leads us to conjecture that the armchair tubes are more easily subject to the opening of the tubular sheets than the zigzag tubes under the existence of a nitrogen source. The hole formation recently proposed by Czerw et al. [Nano Lett. 1, 457 (2001)] is also shown to be energetically favorable. Calculation of the electronic density of states shows that the doping-induced electronic states near the Fermi energy are sensitive to the chirality.