Electronic properties of K-doped single-wall carbon nanotube bundles

We have investigated electronic properties of K-doped single-wall carbon nanotube bundles by the first principles calculations. The lattice expands up to 8% at ${\mathrm{K}}_{0.1}\mathrm{C}$ with negative binding energies, where distortion of tube walls is negligible up to ${\mathrm{K}}_{0.25}\mathrm{C}$ with full relaxation, contrary to the previous reports. Partial charge transfer occurs from potassium atom to the tube. The Fermi level and the amount of charge transfer increase with increasing doping concentration and saturate at large concentration, strongly indicating that the charge transfer is mainly responsible for conductivity increase of the tubes.