Spin magnetism of finite length zigzag carbon nanotubes

By means of model calculations, it is shown that finite zigzag carbon nanotubes with large enough length and diameter possess a ground state with the parallel spin orientation of all electrons, occupying quasi-degenerate (hyperbolic) levels. This trend is weakly affected by the electron interaction, removing orbital degeneracy, and also by the external (ionic crystal) potential. The dependence of total energy on the molecular spin is calculated for carbon nanotubes attached to the neutral surfaces of SiO2 (1 1 0), CdS (1120), and CdTe (1 1 0) crystals.