Effect of nanotube length on the aromaticity of single-wall carbon nanotubes

Density functional theory is used to determine nucleus-independent chemical shift (NICS), an index of local aromaticity, of rings composing single-wall carbon nanotubes of various chiralities and approximately the same diameter as a function of their length. The NICS values of rings in (6, 5) nanotubes do not change much with the tube length, whereas those in nanotubes (5, 5) and (7, 5) change periodically, and the ones in (9, 1) nanotubes change dramatically at certain points. Except for a few special cases of nanotube (9, 1), it is found that two aromaticity criteria, the NICS value and the ring formation energy, agree very well for the first ring at the open end of the tube.