Electron-vibration coupling constants in positively charged fullerene

Recent experiments have shown that C-60 can be positively field doped. In t hat state, fullerene exhibits a higher resistivity and a higher superconduc ting temperature than the corresponding negatively doped state. A strong in tramolecular hole-phonon coupling, connected with the Jahn-Teller effect of the isolated positive ion, is expected to be important for both properties , but the actual coupling strengths are so far unknown. Based on density fu nctional calculations, we determine the linear couplings of the two a(g), s ix g(g) and eight h(g) vibrational modes to the H-u highest occupied molecu lar orbital level of the C-60 molecule. The couplings predict a D-5 distort ion, and an H-u vibronic ground state for C-60(+). They are also used to ge nerate the dimensionless coupling constant lambda which controls the superc onductivity and the phonon contribution to the electrical resistivity in th e crystalline phase. We find that lambda is 1.4 times larger in positively charged C-60 than in the negatively doped case. These results are discussed in the context of the available transport data and superconducting tempera tures. The role of higher orbital degeneracy in superconductivity is also a ddressed.