Electronic polarization in organic molecules and molecular solids: classical interactions between quantum systems – Eugene Tsiper

Date: Mon. March 10th, 2003, 12:30 pm-1:30 pm
Location: Rockefeller 221

Electronic structure of molecular solids is strikingly different from the conventional inorganic semiconductors, such as Si. Coulomb interactions between molecules in van der Waals contact, narrow bandwidths and localized nature of charges make electronic polarization a major effect, with energy scale greater than transfer integrals or temperature. We present an approach which treats individual molecules rigorously as quantum-mechanical systems subject to classical non-uniform fields of all other molecules. Atom-atom polarizability tensor is introduced to describe self-consistent intra-molecular charge redistribution. Dielectric tensors of two representative organic molecular crystals are computed to within experimental accuracy. We find quantitative agreements in charge carrier energetics with photoelectron and STM data. Applications of the approach range broadly from optical and dielectric response of molecular crystals to charge transport energetics in nanoscale molecular devices to hydrogen bonding and intermolecular forces in biosystems. Calculations for crystalline thin films reveal significant differences in electronic polarization at surfaces, metal-organic interfaces, in thin organic layers, and in the bulk, leading to about 0.5 eV transport gap variations across organic films. In the end of the talk I will make brief connections to other areas of my research, which include dynamic mean-field treatment of electronic excitations and Configuration Space Renormalization as an improvement on configuration interaction (CI) methods.