The strength of the electron-phonon interaction has been addressed in several ways, both via ab initio alculations and via analysis of experiment. A very early theoretical estimate was obtained within the rigid muffin-tin approximation (I.I. Mazin et. al, Phys. Rev. B 45, 5114 (1992)), using an empirical phonon model. Later a full potential LMTO calculation was performed to obtain ab initio phonon frequencies, eigenvectors and electron-phonon couplings (Phys. Rev. B 48, 7651 (1993))) in a frozen phonon approach.
The electron-phonon coupling has also been deduced from photoemission measurements for free, negatively charged, C60 molecule. In this approach the coupling strengths are deduced from the weights of the phonon satellites in the photoemission spectrum (Phys. Rev. Lett. 47, 1875 (1995)).
The electron-phonon coupling can also be deduced from Raman scattering data. These estimates differ substantially from the once deduced from photoemission. We have therefore analyzed the methods for extracting the electron-phonon coupling from Raman scattering data and shown that the two types of experiment can be partly reconciled.
To obtain the electron-phonon coupling, it is important to also know the density of states, since this quantity enters as a multiplying factor. Different estimates of density of states have therefore been analyzed.
The theoretical estimates generally give a rather weak coupling to the low-lying Hg phonons in contradiction to the experimental estimates. The reason for this discrepance is not known.