Mechanical and electromechanical coupling in carbon nanotube distortions

A simple approach is presented for using bond-stretching and bond-bending modes to describe the static deformations of carbon nanotubes and related actuation effects. This approach allows us to analyze various phenomena in a unified way and to clarify their relationships. We discuss gap energy modulation by external strains, dimensional and torsional deformations caused by charge injection, and stretch-induced torsion. We show how symmetry determines the property dependence on the chiral angle of nanotubes. Electrically driven actuator responses related to deformation-induced modulation of electron kinetic energy are particularly interesting and relevant for applications. The strong oscillatory dependence of these responses on the nanotube geometry is explained within an intuitively clear picture of bonding patterns. We show how anisotropic (shear) deformations play an important role in nanotubes, making their responses distinctly different from graphite's.