First-principles study on electronic structures and optical properties of the single-walled (n, 0) ZnO nanotubes

Using the first-principles calculations, we studied the geometric structures, electronic structures and optical properties of the single-walled (n, 0) ZnO nanotubes (NTs). The calculated results show that all the bind energies of the single-walled (n, 0) ZnO NTs are of negative values, which indicate that the ZnO NTs can exist stably as single-walled NTs. While the calculated results of electronic structure indicate that the single-walled (n, 0) ZnO NTs are a type of direct wide band-gap semiconductor materials, the whole valence bands are spread and drift to low-energy direction with the increase of the NT diameter. The defect energy levels caused by quantum size and surface effects emerge on the top of the valence bands. Furthermore, the calculated results of optical properties reveal that the dielectric peaks have a blue shift and the edge of absorption band corresponds to ultraviolet band with the decrease of the NT diameter. The single-walled (n, 0) ZnO NTs can be applied to ultraviolet semiconductor systems.