Torsional instability of chiral carbon nanotubes

Abstract

In this work we investigate the presence of a torsional instability in single-wall carbon nanotubes which causes small diameter chiral carbon nanotubes to show natural torsion. To obtain insight into the nature of this instability, the natural torsion is calculated using an extended tight-binding model and is found to decrease as the inverse cube of the diameter. The dependence of the natural torsion on chiral angle is found to be different for metallic and semiconducting nanotubes, specially for near-armchair nanotubes, for which the behavior of semiconducting nanotubes deviates from the simple $\text{sin}(6\ensuremath{\theta})$ behavior observed for metallic nanotubes. The presence of this natural torsion implies a revision of the calculation of the chiral angle of the nanotubes.