Electron-phonon coupling in halogen-doped carbon clathrates from first principles

Electronic structure and electron-phonon coupling of carbon clathrates C₄₀, C₃₄, and C₄₆ doped with interstitial halogen atoms (fluorine, iodine) in the fullerenic cages of the host, have been investigated from first principles. It turns out that, while in C₄₀ and C₄₆ the halogen is only partially reduced, in FC₃₄ an electron is transferred to the guest ion by injecting holes in the valence band of the host. The calculated electron-phonon coupling constant is as large as λ=0.85. We propose that halogen-doped carbon clathrates might represent another form of tetrahedral carbon, in addition to the recently found B-doped diamond, suitable to turn superconductive at high temperature (Tc~770.3em0exK from McMillan formula).