A Computational Study of Armchair Nanotube

Single-walled armchair carbon nanotubes (n,n) of one and two unit cells with n = 3,4,5 and 6 have been studied using semi-empirical PM3 and PM6 methods and an effort has been made to understand the reactivity profiles of these nanotubes. The studied carbon nanotubes are saturated with hydrogen at the ends. Various reactivity descriptors like ionization potential, electron affinity, chemical potential, HOMO-LUMO gap are discussed in terms of the frontier molecular orbitals. The HOMO-LUMO gap is found to decrease with increase of the diameter for one unit cell nanotubes whereas it increases in the case of two unit cells nanotubes. Heat of formation and binding energy per carbon atom are also reported for these nanotubes.