MADELUNG ENERGIES, FORCE-CONSTANTS, AND LOW-ENERGY PHONON DENSITY OF STATES FOR K3C60

The Madelung energies for the different lattice sites of the superconducting K3C60 compound are calculated. The nearest neighbor force constants between C60-K(1), C60-K(2), and C60-C60 are estimated from Madelung energies and Born Mayer ion-ion repulsive potentials and are found to be much smaller than estimated earlier by Zhang, Ogata, and Rice. It is also found that the contribution to the force constant between C60-C60 resulting from valence electrons is important in order to account for the measured bulk modulus. By applying the real space recursion method by Haydock we compute the low energy local phonon density of states. The role of these phonon states for superconductivity is discussed.