The relationship between the band gap and the vacancy density was investigated from first principles. The range influence of a vacancy defect due to structural deformation was characterized and a microscopic explanation was proposed to relate the structural deformation to the band-gap variation. In order to investigate the effect of the defect density upon carbon nanotubes, 5 models of (5,5) armchair carbon nanotubes were built with the defect density being one vacancy per 79, 119, 159, 199 or 239 carbon atoms. The long influence range of a MVD was characterized by structural deformation analysis, and the strain caused by the MVD was found to be the main reason causing the strong fluctuation in band gap of defected armchair single-walled carbon nanotubes. No simple correlation was found between the MVD density and the band gap. The results shed light on the instability of the defected armchair single-walled carbon nanotubes synthesized via ion-bombardment.

Influence of Vacancy Defect Density on Electrical Properties of Armchair Single Wall Carbon Nanotube. L.G.Tien, C.H.Tsai, F.Y.Li, M.H.Lee: Diamond and Related Materials, 2008, 17[4-5], 563-6