Possible charge-ordered states in boron-nitride and boron-carbon-nitride nanotubes and nanoribbons

Electronic states in boron-nitride and boron-carbon-nitride nanoribbons with zigzag edges are studied using the extended Hubbard model with nearest-neighbor Coulomb interactions. Charge- and spin-polarized states are considered, and the phase diagram between two states is obtained. Next ' electric capacitance is calculated to examine the nanofunctionalities of the system. Owing to the presence of strong site energies, the charge polarized state overcomes the spin polarized state, yielding a large difference in the phase diagram compared with that of a graphite system. Electronic structures are always like that of semiconductors. Capacitance is inversely proportional to ribbon width, owing to the presence of the charge excitation energy gap.