Electrical and Mechanical Properties of Twisted Carbon Nanotubes

We have evaluated the energies required to twist carbon nanotubes (NTs), and investigated the effects of these distortions on their electronic structure and electrical properties. The computed distortion energies are high, indicating that it is unlikely that extensive twisting is the result of thermal excitation. Twisting strongly affects the electronic structure of NTs. Normally metallic armchair $(n,n)$ NTs 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 values of the twisting energy and of the band-gap are strongly affected by allowing structural relaxation in the twisted structures. Finally, we have used the Landauer-B{\"u}ttiker formalism to calculate the electrical transport of the metal-NT-metal system as a function of the NT distortion.