The influence of different types of atomic vacancies on the electronic structure of C nanotubes (20, 0) and (12, 12) was investigated by using an empirical tight-binding method. The models with vacancies randomly and symmetrically arranged in an extended unit cell were constructed. The symmetrical distribution of defects was obtained by rotating a pore, obtained by removing a hexagonal ring from a graphitic shell around the tube axis. The random defects were generated by a specially developed algorithm, which eliminates a given number of atoms from the unit cell so that the remaining C atoms have no more than one dangling bond. The presence of vacancies in C nanotube caused an enhancement of density of occupied states that was near the Fermi level and whose localization increased with the number of two-coordinated atoms at the pore boundaries. It was found that the occurrence of atomic vacancies in the C nanotube walls might result in the narrow-gap semiconductors and ferromagnetic materials.

Modifications to the Electronic Structure of Carbon Nanotubes with Symmetric and Random Vacancies. V.V.Belavin, L.G.Bulusheva, A.V.Okotrub: International Journal of Quantum Chemistry, 2004, 96[3], 239-46