Electrical and mechanical properties of distorted carbon nanotubes

We have calculated the effects of structural distortions of armchair carbon nanotubes on their electronic and electrical properties. We found that the bending of the nanotubes decreases their transmission function in certain energy ranges and leads to an increased electrical resistance. Electronic structure calculations show that these energy ranges contain localized states with significant $\ensuremath{\sigma}\ensuremath{-}\ensuremath{\pi}$ hybridization resulting from the increased curvature produced by bending. Twisting strongly affects the electronic structure of nanotubes (NTs). Normally metallic armchair $(n,n)$ NT's develop a band gap which initially scales linearly with twisting angle and then reaches a constant value. This saturation is associated with a structural transition to a flattened helical structure. The computed values of the twisting energy and of the band gap are strongly affected by allowing structural relaxation in the twisted structures. Finally, our calculations show that the large contact resistances observed for single-wall NT's are likely due to the weak coupling of the NT to the metal in side bonded NT-metal configurations.