Jahn-Teller distortion of ionized and excited carbon nanotubes

Due to their rotational (C-n) symmetry, neutral zigzag and armchair type nanotubes possess doubly degenerate orbitals. As the energies of highest occupied molecular orbital and lowest unoccupied molecular orbital are usually different, neutral nanotubes exhibit a nondegenerate ground state. Ionized or excited forms of these tubes, however, may undergo Jahn-Teller distortion if degenerate orbitals show up in the vicinity of the Fermi level. Theoretical calculations in a simple one-eletron-per-site model show that the Jahn-Teller distortion energies are in order-of-magnitude of 0.1 eV for short pieces of tubes, and are associated with a significant geometry change. Distortions tend to diminish quickly with increasing tube length, except if multiple ionizations are considered.