  The proposal of using the field-effect for doping organic crystals has raised
enormous interest. To assess the feasibility of such an approach, we
investigate the effect of a strong electric field on the electronic structure
of C60 crystals. Calculating the polarization of the molecules and the
splittings of the molecular levels as a function of the external field, we
determine up to what field-strengths the electronic structure of C60 stays
essentially unchanged, so that one can speak of field-effect doping, in the
sense of putting charge carriers into otherwise unchanged states. Beyond these
field strengths, the electronic structure changes so much, that on can no
longer speak of a doped system.
  In addition, we address the question of a metal-insulator transition at
integer dopings and briefly review proposed mechanisms for explaining an
increase of the superconducting transition temperature in field-doped C60 that
is intercalated with haloform molecules.
