Band structure and optical properties of isolated and bundled nanotubes

We studied the electronic band structure of isolated and bundled single‐walled nanotubes by ab initio calculations. Curvature effects on the electronic states depend on the chirality of the nanotube; the strongest deviations from the zone‐folding approximation are found in zig‐zag tubes. Bundling of the tubes to ropes further reduces the band gap in semiconducting tubes (20 – 30 %). We present first‐principles calculations of the optical absorption spectra in a (19,0) nanotube.