First-principles study of the optical properties of ZnO single-wall nanotubes

We report simulations of the electronic structures and optical properties of ZnO single-wall nanotubes (SWNTs) within a first-principles, local-density functional approach adapted for helical symmetry. Recent theoretical reports have addressed the possibility of ZnO existing in flat graphitic-like sheets as well as a single-wall nanotubular structures analogous to carbon nanotubes. We present results for a range of different ZnO SWNTs, both chiral and achiral, with radii ranging from approximately 2.10 to 5.02 angstrom. Optical cross-sections for these nanostructures were estimated on the basis of the first-principles electronic structure results. The optical absorption spectra exhibited a first optical absorption peak associated with a direct transition that remained relatively stationary as nanotube radius varied but with a second direct optical peak blue-shifting with decreasing nanotube radius.