Formation energies of topological defects in carbon nanotubes

Tight-binding calculations are presented for the formation energies of a ty pe of topological defect called the 5-77-5 defect in achiral carbon nanotub es. The calculations show that the defect formation energy is dependent on the chirality and radius of a tube as well as the different orientations of a 5-77-5 defect in a tube. We also presented trends of the defect formatio n energy varying with tube size in the whole size range of the achiral carb on nanotubes. Moreover, it is indicated that a positive bond length deviati on originating from a 5-77-5 defect in a tube can improve the sp(2)-like hy bridization towards sp(2) hybridization locally, which enhances the stabili ty of the system.