SCREENED INTERACTION AND COULOMB PSEUDO-POTENTIAL IN C-60

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 approximately 0.05 eV), leading to mu = UN(0) approximately 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 u* may not be much smaller than mu approximately 0.4 in C60. To obtain reasonable transition temperatures, T(c), this value of mu* (approximately 0.4) requires values of the electron-phonon coupling constant lambda, which are not very much larger than what has been calculated.