title: A new efficient method for calculation of Frenkel exciton parameters in molecular aggregates.
abstract: The Frenkel exciton Hamiltonian is at the heart of many simulations of excitation energy transfer in molecular aggregates. It separates the aggregate into Coulomb-coupled monomers. Here it is shown that the respective parameters, i.e., monomeric excitation energies and Coulomb couplings between transition densities can be efficiently calculated using time-dependent tight-binding-based density functional theory (TD-DFTB). Specifically, Coulomb couplings are expressed in terms of self-consistently determined Mulliken transition charges. The approach is applied to two dimer systems. First, formaldehyde oxime for which a detailed comparison with standard DFT using the B3LYP and the PBE functionals as well as with SCS-CC2 is provided. Second, the Coulomb coupling is explored in dependence on the intermolecular coordinates for a perylene bisimide dimer. This provides structural evidence for the previously observed biphasic aggregation behavior of this dye.
authors.affiliation: Institut für Physik, Universität Rostock, D-18051 Rostock, Germany.
authors.forename: Per-Arno
authors.initials: PA
authors.lastname: Plötz
authors.affiliation: Institut I - Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Niehaus
authors.affiliation: Institut für Physik, Universität Rostock, D-18051 Rostock, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Kühn