Tight-binding parametrization of first-principles electronic dispersion in orientationally disorderedA3C60

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