Optical absorption spectra and polarizabilities of silicon carbide nanotubes: A first principles study

We have calculated the optical absorption spectra and polarizabilities of silicon carbide nanotubes by using the density functional theory within the local density approximation. Most of the examined single-walled silicon carbide nanotubes (SWSiCNTs) exhibit the first strong absorption peak around 3 eV, while the ultrathin (5 0) SWSiCNT exhibits the first three strong peaks in the 1.5-4.0 eV region. The screened polarizabilities of SWSiCNTs are contributed by the localized valence electrons and can be described by a classical dielectric cylindrical shell model, compared with the delocalized pi-electrons and the semimetallic shell model of carbon nanotubes. The longitudinal screened polarizabilities of SWSiCNTs are apparently larger than the transverse ones by a factor of 3.5-8.1, suggesting the possibility of their aligned synthesis in electric fields. In multiwalled silicon carbide nanotubes, the inner tube is partially shielded by the outer tube for light polarized perpendicular to the tube axis, compared with the nearly complete shielding effects in multiwalled carbon nanotubes.