ORIGINAL PAPER Carbon Doping of Defect Sites in Stone–Wales Defective Boron-nitride Nanotubes: A Density Functional Theory Study Maryam Anafcheh • Reza Ghafouri Received: 16 February 2013 Ó Springer Science+Business Media New York 2013 Abstract We have performed a density functional theory study to investigate the effect of carbon doping on Stone–Wales (SW) defective sites in the armchair (4, 4), (5, 5) and (6, 6) BNNTs, in order to remove structural instability induced by homonuclear N–N and B–B bonds. Two different orientations of SW defect are considered, parallel and diagonal, and then C atoms are doped at different positions of the defect sites. In general, it seems that among the considered arrangements, C atoms prefer to be substituted for the homonuclear B–B bond. The larger HOMO– LUMO band gaps for the most stable configurations indicate that C doping at B–B sites is kinetically more favorable than the other ones. According to calculated nuclear quadrupole resonance (NQR) parameters as a result of C-doping on SW defective sites, the quadrupole coupling constants (C Q ) of boron nuclei at defective sites decrease by about 0.508–1.406 MHz while 14 N C Q of the defective sites, except for N 8 , increases. Interestingly, C Q of the N sites directly connected to dopant sites has maximum increment (0.612–2.596 MHz) while C Q of the N sites belonging to the B 2 N 3 pentagon is undergone to some minor changes. Keywords Stone–Wales defect  Doping  BNNTs  DOS  NQR  DFT Introduction Single walled nanotubes (SWNTs) were first considered as perfect seamless cylindrical graphene-like network—a defect-free structure. However, after more Electronic supplementary material The online version of this article (doi:10.1007/s10876-013-0584-1) contains supplementary material, which is available to authorized users. M. Anafcheh  R. Ghafouri (&) Department of Chemistry, Shahr-e-Ray Branch, Islamic Azad University, Tehran, Iran e-mail: reghafouri@gmail.com 123 J Clust Sci DOI 10.1007/s10876-013-0584-1