The relative stability of a family of carbon nanotubes with defects was investigated theoretically using first-principles density functional theory calculations, B3LYP/6-31G*. A set of (12,0)-(8,0) heterojunctions with an increasing number (n = 1 to 4) of pentagon/heptagon defects was studied systematically in various arrangements, and the results were compared with a set of small defective graphene fragments. In addition, tubular structures with two pairs of variously distributed defects (along and around the carbon nanotube) at increasing distances were considered. Within the defective structures, those containing the well-known Stone-Wales defect proved to be the most stable. However, when more than two pairs of defects co-existed, situations where the defects appeared together seemed to be preferred, in sharp contrast to the isolated pentagon rule for fullerenes; although this agreed with some previous work on the topic. The junctions studied here constituted various arrangements that helped to identify which effects (geometry, energy) arose from the particular positions and orientations of the defects. A close correlation was found between the energy stability and the geometric deformation, measured in terms of the average pyramidization angle and the average trigonal deformation.

Causes of Energy Destabilization in Carbon Nanotubes with Topological Defects. F.J.Martín-Martínez, S.Melchor, J.A.Dobado: Theoretical Chemistry Accounts, 2011, 128[4], 445-56