Density functional calculations for C60 peapods

Nanotubes filled with C60 molecules, commonly referred to as peapods, are studied using the local density approximation of the density functional theory. The band structure of the peapods are investigated in detail, concentrating in particular on the C60 derived bands and their hybridization with the nanotube bands. It is found that the t1u states of fullerene are always located close to the Fermi level or midgap for metallic and insulating nanotubes, respectively. This is a consequence of the strong electron affinity of the C60 molecule. For insulating nanotubes, the t1g states, on the other hand, are located roughly in the energy region of the third van Hoove singularity, resulting in some degree of hybridization, if the corresponding nanotube states possess the proper symmetry. Except for narrow nanotubes, simulated scanning tunneling spectroscopy images of the peapods show a very low contrast for C60 derived states.