Common electronic band gaps and similar optical properties of ZnO nanotubes

Electronic and optical properties of single-walled zinc oxide (ZnO)nanotubes are investigated from the first-principles calculations.Electronic structure calculations show that ZnO nanotubes are alldirect band gap semiconducting nanotubes and the band gaps arerelatively insensitive to the diameter and chirality of tubes. Theorigin of the common electronic band gaps of ZnO nanotubes isexplained in terms of band-folding from the two-dimensional bandstructure of graphite-like sheet. Moreover, the optical propertiessuch as dielectric function and energy loss function spectra ofdifferent ZnO nanotubes are very similar, relatively independent ofdiameter and chirality of tubes. The calculated dielectric functionand loss function spectra show a moderate optical anisotropy withrespect to light polarization.