Strongly size-dependent electronic properties in C60-encapsulated zigzag nanotubes and lower size limit of carbon nanopeapods -: art. no. 121402

By using first-principles calculations, we found that the electronic structures near the Fermi level of the nanotubes rigidly filled by a loose-packed fullerene chain can be approximated by a sum of those of the two constituents that are rigidly relatively shifted. Extending this rigid band shift approximation to the (n,0) nanotubes rigidly filled by a close-packed C-60 chain, a dramatic change in electronic properties from semiconductor (n=17) to metal (n=18 and 19) is seen, and the recently observed fine double peak structure on the conduction band of the semiconducting nanotube induced by C-60 encapsulation is well reproduced. The theoretical smallest diameter of a nanopeapod is 10.64 Angstrom.