  We present an approach to electronic polarization in molecular solids treated
as a set of quantum systems interacting classically. Individual molecules are
dealt with rigorously as quantum-mechanical systems subject to classical
external fields created by all other molecules and, possibly, external sources.
Self-consistent equations are derived for induced dipoles and for atomic
charges whose redistribution in external fields is given explicitly by an
atom-atom polarizability tensor. Electronic polarization is studied in two
representative organic molecular crystals, anthracene and
perylenetetracarboxylic acid dianhydride (PTCDA), and contrasted to previous
results for systems of polarizable points. The stabilization energies of the
neutral lattice, of isolated anions and cations, and of cation-anion pairs are
found. Charge redistribution on ions is included. The dielectric tensors of
crystals are successfully related to gas-phase properties and provide
consistency checks on polarization energies. The procedure is generally
applicable to organic crystals in the limit of no intermolecular overlap.
