Tight-Binding Parametrization of First-Principles Electronic Dispersion in Orientationally Disordered A3c60

We derive numerical tight-binding hopping parameters to describe conduction-band dispersion in arbitrary orientational phases of $A_3$C$_{60}$. The parameters are obtained by direct Fourier inversion of the spectra from self-consistent electronic-structure calculations for K$_3$C$_{60}$ using the local-density approximation, including the effects of orientational dependence. Using the new parameters, we revisit several earlier investigations of the orientational ordering in $A_3$C$_{60}$; some of the earlier results are substantiated, while others are slightly modified.