Abstract
Various carbon materials have been discovered in recent years, and their characteristics are remarkably interested in applications to new devices. In particular, the investigation of carbon nanomaterials has markedly progressed in physics and in industry. In many studies, conduction bands in carbon sheets have been treated as the antibonding states of sp2 orbitals. In contrast, in this work, excited states as in the Hubbard model are assumed and are added to the previous ground states. These excited states are set as singlet spin states composed of 2pz (3s) orbitals, which have the same character as the valence bond singlet spin state. The electronic structures of these materials are calculated on the basis of the LCVB tight-binding theory. The calculated results clearly explain the energy states of benzene. The conductive states in graphite sheets are also accurately obtained from the experimental data by including the proposed excited states. The electronic structures of nanotubes are characterized with several types of compositions related to band gaps and the Fermi levels. The characteristic sharp peak adjacent to the Fermi level in the conduction band is realistically represented in each calculation.
