Atomic multipolar contributions to electronic polarization in organic molecular crystals

The self-consistent computation of electronic polarization in organic molecular crystals is extended to include, in first order, corrections in the continuous gas-phase charge distribution ρ G ( r ). The potential ΔΦ a ( r a ) at molecule a in the crystal is due to the difference between ρ G ( r ) and a point-charge approximation. ΔΦ a ( r a ), which represents atomic multipolar contributions, is evaluated for crystals of anthracene and perylenetetracarboxylic dianhydride (PTCDA). The corrections to the polarization energies of molecular cations are P + (1) = -0.25 and -0.14 eV for anthracene and PTCDA, respectively, while P − (1) = 0.25 and 0.18 eV for the anions. The leading term of atomic multipoles is the ΔΦ a ( r a )-charge interaction that corresponds to the charge-quadrupole term in the submolecular approach. There are also new contributions in ΔΦ a ( r a )-redistributed charge and coupling of induced dipoles to gradients of ΔΦ a ( r a ). First-order correction to electronic polarization is a general approach that combines the advantages of discrete charges for self-consistent treatment of crystals with accurate electrostatic potentials based on the best available molecular charge distribution.