Electronic structure properties of carbon nanotubes obtained by density functional calculations

The total energies, atomic charges, and energy band gaps of (3,3) and (7,7) armchair and (6,0) and (12,0) zig-zag carbon nanotubes (CNTs) of various lengths were determined using density functional ab initio (DFT) calculations. Armchair CNTs were found to be less reactive than zig-zag CNTs. The calculated band gap, which accounts for metallic character, was smaller in (3n,0) zig-zag tubes than in armchair CNTs and in both cases the band gaps decreased with increasing lengths of the tubes. However, frontier orbitals, which account for conductivity, were localized in zig-zag but delocalized in armchair tubes.