Exploring the simultaneous existence of Stone-Wales and carbon ad-dimer defects in the zigzag single-walled carbon nanotubes

We have applied density functional calculations to investigate simultaneous existence of Stone Wales (SW) and carbon ad-dimer (CD) defects in the zigzag (n, 0) n=5, 6, 7, 8, 9, and 10 SWCNTs, with an extensive search by considering two different orientations of defects. According to our results, the adsorption of a carbon dimer on a hexagonal ring of SWCNTs is easier than the rotation of a C C bond trough the SW rearrangement. Moreover, the formation of a carbon dimer on the exterior sidewalls of an SW defective SWCNT or the rotation of a C C bond of a CD defective SWCNT is more favorable than those on the perfect ones. Defect formation energy shows a strong dependence on the both SWCNT radius and defect orientation. The reactivity of SW CD defective SWCNTs through chemisorption of hydrogen atoms on the central bonds of defect sites shows the thermodynamically lower preference of additions for the CD defective sites in comparison to SW defective sites. Histograms of the 13C NMR chemical shifts of SW CD defective SWCNTs exhibit individual signals for defect sites, which can be attributed to azupyreneand pentalelene-like structures for SW and CD defect sites, respectively. (C) 2016 Elsevier B.V. All rights reserved.