It was noted that the introduction of a pentagon–heptagon pair defect into the perfect hexagonal network of two C nanotubes could change the helicity of the tube and alter its electronic structure. By using a tight binding method to calculate the electronic structure of such a system, it was shown that this pentagon–heptagon pair defect in the nanotube structure was not only responsible for the change in nanotube diameter, but also governed the electronic behavior around the Fermi level.

Electronic Properties of Carbon Nanotubes with Pentagon–Heptagon Pair Defects. H.F.Hu, Y.B.Li, H.B.He: Diamond and Related Materials, 2001, 10[9-10], 1818-23