Electron energy spectrum and peculiarities of optical absorption of double-walled carbon nanotubes doped by alkali metals atomsArkadiy Ovseevich Litinskiy and Vitaly Vladimirovich KamnevEur. Phys. J. B, 86 5 (2013) 219DOI: https://doi.org/10.1140/epjb/e2013-31027-3