Carbon-nanotube geometries as optimal configurations

The fine geometry of carbon nanotubes is investigated from the viewpoint of Molecular Mechanics. Actual nanotube configurations are characterized as being locally minimizing a given configurational energy, including both two- and three-body contributions. By focusing on so-called zigzag and armchair topologies, we prove that the configurational energy is strictly minimized within specific, one-parameter families of periodic configurations. Such optimal configurations are checked to be stable with respect to a large class of small nonperiodic perturbations and do not coincide with classical rolled-up nor polyhedral geometries.