Theoretical study of N-complexes in carbon nanotubes

We have made a systematic theoretical study to determine which are the most stable structures for substitutional nitrogen defects in carbon nanotubes, by making total energy calculations via DFT. These calculations were made for a (5,5) and a (8,0) nanotube to check the influence of chirality and for a graphene sheet, to check the limit of infinite diameter. In all these systems, we found that either substitutional nitrogen or structures containing two vacancies surrounded by four pyridine-like rings have the lowest formation energy, depending on the value of the nitrogen chemical potential. These defects have lower formation energies in nanotubes than in the graphene sheet.