Orbital Hybridization and Charge Transfer in Carbon Nanopeapods

We investigate the electronic structure of the fullerenes encapsulated inside carbon nanotubes, the so-called nanopeapods, using the first-principles study. The orbital hybridization of $\mathrm{L}\mathrm{U}\mathrm{M}\mathrm{O}+1$ (the state above the lowest unoccupied molecular orbital) of ${\mathrm{C}}_{\mathrm{60}}$, rather than LUMO as previously proposed, with the nanotube states explains the peak at $\sim 1\mathrm{e}\mathrm{V}$ in recent scanning-tunneling-spectroscopy (STS) data. For the endohedral metallofullerenes nested in the strained nanotube, the charge transfer shifts the relative energy levels of the different states and produces a spatial modulation of the energy gap in agreement with another STS experiment.