Vibronic coupling constants in BEDT-TTF and C60

The results of a fullyab-initio determination of the vibronic coupling strengths in molecular and organic superconductors based on C₆₀ and BEDT-TTF are presented, with the vibrational and the electronic structure treated on an equal footing. We obtain accurate vibrational frequencies, and the corresponding coupling constants are obtained without parameters. We examine the implications of the coupling constants in relation to the molecular vibronic coupling theories of superconductivity in these materials. We find that for C₆₀^3– the coupling to both the low- and high-frequency molecular modes are important. For the BEDT-TTF-based organic superconductors the effects of isotope substitution are also examined.