It was shown that the two different orientations of Stone-Wales defects, i.e. longitudinal and circumferential, on carbon nanotubes resulted in two different electronic structures. Based upon density functional theory it was shown that the longitudinal Stone-Wales defects did not open a band gap near to the Fermi energy, while a relatively small band gap appeared for tubes with circumferential defects. It was argued that the band-gap opening in the presence of circumferential Stone-Wales defects was a consequence of long-range symmetry breaking which could spread all the way along the tube. Specifically, the distribution of contracted and stretched bond lengths due to the presence of defects, and hopping energies for low-energy electrons, i.e. the 2p z electrons, exhibited two different patterns for the two types of defect. Interplay between the geometric features and the electronic properties of the tubes were also studied for various defect concentrations. Considering the orbital charge density, it was also shown that the deviations of bond lengths from their relaxed length resulted in differing doping for two defect orientations around the defects: electron-rich for a circumferential defect and hole-rich for a longitudinal one. It was also shown that, in tubes having both types of defect, circumferential defects would dominate and impose their electronic properties.

Stone-Wales Defects Can Cause a Metal-Semiconductor Transition in Carbon Nanotubes Depending on Their Orientation. P.Partovi-Azar, A.Namiranian: Journal of Physics Condensed Matter, 2012, 24[3], 035301