title: Spectral densities for Frenkel exciton dynamics in molecular crystals: A TD-DFTB approach.
abstract: Effects of thermal fluctuations on the electronic excitation energies and intermonomeric Coulomb couplings are investigated for a perylene-tetracarboxylic-diimide crystal. To this end, time dependent density functional theory based tight binding (TD-DFTB) in the linear response formulation is used in combination with electronic ground state classical molecular dynamics. As a result, a parametrized Frenkel exciton Hamiltonian is obtained, with the effect of exciton-vibrational coupling being described by spectral densities. Employing dynamically defined normal modes, these spectral densities are analyzed in great detail, thus providing insight into the effect of specific intramolecular motions on excitation energies and Coulomb couplings. This distinguishes the present method from approaches using fixed transition densities. The efficiency by which intramolecular contributions to the spectral density can be calculated is a clear advantage of this method as compared with standard TD-DFT.
authors.affiliation: Institut für Physik, Universität Rostock, Albert Einstein Strasse 23-24, D-18059 Rostock, Germany.
authors.forename: Per-Arno
authors.identifier: 0000000272134046
authors.initials: PA
authors.lastname: Plötz
authors.affiliation: Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Potsdam, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Megow
authors.affiliation: Institut Lumière Matière, Université Lyon, Université Claude Bernard Lyon 1, CNRS, F-69622 Villeurbanne, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Niehaus
authors.affiliation: Institut für Physik, Universität Rostock, Albert Einstein Strasse 23-24, D-18059 Rostock, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Kühn