Quasiparticle band structure of carbon nanotubes

We study the electronic structure of carbon nanotubes theoretically by first-principles techniques. Geometry is optimized with the local-density approximation (LDA) in density functional theory, and many-body effects between electrons are taken into account within the GW approximation. We find that the (5,0) tube is metallic even at the GW level, being different from the tight-binding result. The (6,0) tube is also confirmed to be metallic. The GW correction to LDA is found to be small in metallic tubes. The (7,0) tube is semiconducting, in which the GW correction considerably increases the gap. On the other hand, the GW correction is small in graphene, suggesting that the density functional theory gives a reasonable description of large nanotubes.