  We investigate the possibility of doping C60 crystals by applying a strong
electric field. For an accurate description of a C60 field-effect device we
introduce a multipole expansion of the field, the response of the C60
molecules, and the Stark splitting of the molecular levels. The relevant
response coefficients and splittings are calculated ab initio for several high
symmetry orientations. Using a group theoretic analysis we extend these results
to arbitrary orientations of the C60 molecules with respect to the external
field. We find that, surprisingly, for the highest occupied (HOMO) and the
lowest unoccupied molecular orbital (LUMO), respectively, the two leading
multipole components lift the degeneracy of the molecular level in the same
way. Moreover the relative signs of the splittings turn out to be such that the
splittings add up when the external field induces charge into the respective
level. That means that when charge carriers are put into a level, its
electronic structure is strongly modified. Therefore, in general, in C60
field-effect devices charge is not simply put into otherwise unchanged bands,
so already because of this their physics should be quite different from that of
the alkali-doped fullerenes.
