Abstract Submitted to the NANOTUBE'02 Workshop:

We present ab initio calculations of the electronic band structure in carbon nanotubes of different chirality with diameters between 0.8 and 1.5 nm. The curvature of the nanotube walls shifts the conduction and valence bands toward the Fermi level when compared to a zone-folding approximation.[1] The effect depends not only on the nanotube diameter, but also on its chirality: Whereas the band structure of an armchair (10,10) nanotube is very well described by zone-folding, deviations around 100 meV were found for the (19,0) zig-zag tube. Bundling of the nanotubes further shifts the electronic states at the Gamma point. More importantly, however, the tube-tube interaction leads to an intratube dispersion perpendicular to the z axis which is of similar strength as in other pi bonded carbon materials (100-1000 meV). From the first-principles band structure we obtained the optical absorption spectra of individual and bundled single-walled nanotubes. The individual tubes show a series of square-root singularities in the optical absorption coefficient strongly dependent on the polarization direction of the incoming light. In bundled nanotubes, in contrast, the singularities are completely smeared out by the intratube dispersion. Our calculations are in excellent agreement with recent absorption measurements on bundled and soluted single-walled nanotubes.[2]

References:
[1] S. Reich, C. Thomsen, and P. Ordejon, Phys. Rev. B 65 (2002), in print
[2] R. H. Hauge et al., in Proceedings of the XVI International Winterschool on the Electronic Properties of Novel Materials, edited by H. Kuzmany, J. Fink, M. Mehring, and S. Roth (AIP, Woodbury, New York, 2002)