Manifestation of aromaticity and its effects on the electronic structure of finite single-wall carbon nanotubes

Finite single-wall carbon nanotubes (p, q). characterized by p = n + l + 1, q = n - l, 0 less than or equal to l less than or equal to n, and n = 1, 2, ..., consisting of even nanotube (NT) sections may be viewed as a chain of aromatic 'molecules' with each 'molecular-unit' consisting of two NT sections of 4n + 2 sp(2)-bonded carbon atoms. Such (group II) NTs. have large energy gaps for short tubes, whereas for tubes of intermediate lengths, the energy gap decreases monotonically as a function of NT length. The energy gap behaviors are totally different from the previously studied group I NTs with p = n + l and q = n - 1, which exhibited oscillatory characteristics. (C) 2002 Published by Elsevier Science B.V.