First-principles study of the size-dependent structural and electronic properties of thick-walled ZnO nanotubes

The size dependence of atomic relaxations, formation energies, and electronic structures of hexagonal [0001] zinc oxide (ZnO) nanotubes with diameters of up to 2.3 nm were studied using density-functional calculations. The formation energies per Zn–O pair in thick-walled hexagonal ZnO nanotubes were found to be mainly dependent on the wall thickness and not on the tube diameter. Thick-walled ZnO nanotubes are energetically more favorable than single-walled ZnO nanotubes. All ZnO nanotubes were found to be semiconducting, with band gaps larger than that of bulk ZnO. It was also found that the wall thickness of ZnO nanotubes strongly affects their shapes and the energies of the conduction bands, rather than their valence band maxima