O. Gunnarsson, D. Rainer and G. Zwicknagl
Max-Planck-Institut für Festkörperforschung, Stuttgart
We study the screening for C60 in the random phase approximation. For a free molecule we find a substantial reduction of the interaction between close atoms but an ``antiscreening'' of the interaction between distant atoms. For a C60 solid there is an efficient screening of the intraband Coulomb interaction (U~0.05 eV), leading to mu=UN(0)~0.4, where N(0) is the density of states per spin and molecule. We then study the renormalization of the Coulomb pseudo-potential mu* due to higher subbands in a simple two-band model. We find that the renormalization is small, although a traditional approach, summing ladder diagrams in the screened interaction, predicts a large renormalization. This suggests that mu* may not be much smaller than mu~0.4 in C60, where mu* has been renormalized down to the t1u band edge. To obtain reasonable transition temperatures, Tc, this value of mu*(~0.4) requires values of the electron-phonon coupling constant lambda, which are not very much larger than what has been calculated.
Int. J. Mod. Phys. B 6, 3993 (1992).