The authors discuss the geometries of crystalline FCC C60 for three cases of directional order, the hypothetical unidirectional structure with space group Fm3, the bidirectional structure (P42/mnm) which is the ordered version of the structure observed for alkali-metal-doped compounds at room temperature, and the quadridirectional, low-temperature structure (Pa3) of pure C60. Analytical, parameter-free expressions for the t1u wave functions are derived and used to obtain analytical conduction-band Hamiltonians for all three structures. The interactions with other subbands are included in numerical tight-binding calculations with a basis of 60 radial carbon orbitals per molecule. Ab initio density-functional (local-density approximation (LDA)) calculations are performed for unidirectional FCC C60 and RbC60 for different lattice constants. The authors use the linear-muffin-tin-orbitals (LMTO) method in the atomic-spheres approximation with carefully chosen interstitial spheres. The LDA bands are compared with photoemission and inverse photoemission data for C60. For RbC60 they find that the alkali-metal atom is fully ionized and that the doped electron occupies the t1u band in a rigid-band-like fashion. Tight-binding theory explains why, and indicates that this holds generally for An-xBxC60 with n 

Physical Review B, 46 1773-93, 1992.