Using combined “$\text{LDA}+\text{image}$ potential” calculations we show that below the vacuum level a single graphene layer possesses a double Rydberg series of even $\left(n^{+}\right)$ and odd $\left(n^{-}\right)$ symmetry image-potential states and argue that the widely discussed interlayer band in graphite is a consequence of the intersheet hybridization of the first even image-potential state. In light of the present results, the unoccupied electronic states with nearly-free-electron properties in carbon nanotubes, fullerenes, and fullerites can be understood to originate from the image-potential states of graphene.

• Received 20 August 2009

DOI:https://doi.org/10.1103/PhysRevB.80.121408