Comparative study of the optical properties of single-walled carbon nanotubes within orthogonal and nonorthogonal tight-binding models

The dielectric response function of single-walled carbon nanotubes is calculated within tight-binding models with different levels of complexity. First, the effects of the orbital basis set of the model, the orbitals overlap, and the structural optimization on the electronic band structure and the dielectric function of three small-radius nanotubes are investigated in detail. Second, the optical transition energies for a large number of nanotubes are derived from the peak positions of the imaginary part of the dielectric function for parallel and perpendicular light polarization. These results can be useful for the assignment of absorption spectra of nanotube samples and for the determination of the conditions for resonant Raman scattering from nanotubes. The obtained results are compared to recent spectrofluorimetric data on isolated single-walled carbon nanotubes.