STRUCTURAL AND ELECTRONIC-PROPERTIES OF PENTAGON-HEPTAGON PAIR DEFECTS IN CARBON NANOTUBES

General features of the energetics and electronic states of carbon nan otubes, containing pentagon-heptagon pair (5/7) topological defects in the hexagonal network of the zigzag configuration, are investigated w ithin simple tight-binding models. This 5/7 pair defect on the nanotub e structure is not only responsible for a change in nanotube diameter, but also governs the electronic behavior around the Fermi level. Furt hermore, nanotubes having different helicities and different electroni c properties can be connected using such a pair. Various configuration s including one, two, and three 5/7 pairs are explored in order to und erstand the influence of several defects on the electronic properties of the system. Topological aspects associated with the presence of 5/7 pair defects in armchair and chiral nanotubes are also discussed.