Ab-initio calculations 1 for K 3 C 60 indicate that the general features of the energy bands within LDA remain nearly unchanged as compared to C 60 . In the electronphonon pairing mechanism of superconductivity in these materials, the variation in T c has been attributed to changes in the lattice constant 2 which affects N(E F ). We have therefore fitted the valence and conduction bands of the fcc C60, obtained by Troullier and Martins 3 from an LDA plane wave basis calculations, with a tight binding model and studied the energy bands as a function of the lattice constant. As the overlap between orbitals on neighbouring balls is small, the band width is found to decrease by about 30% in going from K 3 C 60 to Rb 2 CsC 60 . The density of states, thus, obtained is used to estimate variation in T c from McMillan's formula. These results are in good agreement with experimental data. Calculations of the energy bands are also presented for the low temperature [Formula: see text] structure.