Long-Range Embedding of Molecular Ions and Excitations in a Polarizable Molecular Environment

We present a method
for evaluating electrostatic and polarization
energies of a localized charge, charge transfer state, or exciton
embedded in a neutral molecular environment. The approach extends
the Ewald summation technique to polarization effects, rigorously
accounts for the long-range nature of the charge-quadrupole interactions,
and addresses aperiodic embedding of the charged molecular cluster
and its polarization cloud in a periodic environment. We illustrate
the method by evaluating the density of states and ionization energies
in thin films and heterostructures of organic semiconductors. By accounting
for long-range mesoscale fields, we obtain the ionization energies
in both crystalline and mesoscopically amorphous systems with high
accuracy.