Effects of nitrogenation on single-walled carbon nanotubes within density functional theory

The effects of nitrogenation on single-walled carbon nanotubes are investigated within the ab initio density functional theory. Four different types of nitrogenation have been considered: (i) direct substitution of nitrogen atoms, (ii) substitution with a formation of vacancy (pyridinelike doping), (iii) exohedral chemisorption of N adatoms, and (iv) sidewall covalent -$\mathrm{N}{\mathrm{H}}_{2}$ functionalization. Structural deformations, electronic band structures, density of states, and ionization potential energies are calculated and compared among the different types of nitrogenated nanotubes. Magnetism is observed for chemisorbed single-walled carbon nanotubes (SWNTs) with magnetic moment of $0.7\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}$. In addition, the relaxed structures of SWNTs with two neighboring chemisorbed N adatoms are generally more complex than those of singly chemisorbed N adatom. The barrier energies needed to coalesce two N adatoms chemisorbed on SWNTs to form a free ${\mathrm{N}}_{2}$ molecule are higher than those for a graphene sheet.