Modification of the electronic structure in a carbon nanotube with the   charge dopant encapsulation
  We present the first-principles study of effects of the charge dopants such as Cesium and Iodine encapsulated on the electronic structure of carbon nanotubes. An encapsulated cesium atom donates an electron to the nanotube and produces donor-like states below the conduction bands. In contrast, an iodine trimer (I$_{3}$) accepts an electron from the nanotube and produces an acceptor-like state above the valance band maximum. We find that a Cs atom inside a metallic armchair carbon nanotube gives rise to spatial oscillations of the density of states near the Fermi level. 
Woon Ih Choi, Jisoon Ihm, and Gunn Kim