First-principles studies of structural, electronic and optical properties of AB2 (A = Si, Ge and B = O, S) nanotubes

The structural, electronic and optical properties of AB2 (A = Si, Ge and B = O, S) nanotubes have been investigated by the first-principles calculations. The one-dimensional SiO2 nanotubes are predicted to be insulators with the large band gaps (∼6 eV), while other tubes are semiconductors. The four types of nanotubes, especially for the SiS2-4 nanotube with a large absorption coefficient (∼1.50 × 105 cm−1), generally exhibit strong absorption in UV region. The size dependences of optical properties on the tube-diameter are remarkable for SiO2, SiS2, and GeS2 nanotubes, while the absorption spectra in parallel (0 0 1) direction of GeO2 nanotubes are less sensitive to the radius of nanotube.