Hamburg 2001 – scientific programme

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SYOF: Organische Festkörper

SYOF 5: Poster Session

SYOF 5.32: Poster

Tuesday, March 27, 2001, 17:00–19:00, Aula S3

Modelling of the Optical Properties of PTCDA: Evidence for Davydov Splitting — •Igor Vragovic, Reinhard Scholz, Andrei Kobitski, and Michael Schreiber — Institut für Physik, Technische Universität, Chemnitz, Germany

The linear absorption of PTCDA crystals is analysed with a Frenkel exciton Hamiltonian for the 3D crystal with two molecules per unit cell, extending previous quasi-1D stack models [M. Hoffmann et al., Chem.Phys. 258, 73-96 (2000)]. The excitons are strongly coupled with internal vibrations, modelled as a Poisson progression for a single effective mode. The exciton transfer between the neigbours along the stack is estimated from density functional calculations for PTCDA dimers, while interactions between more distant molecules are calculated in point-dipole approximation.

It is shown in detail how the different classes of intermolecular interactions lead to a pronaunced deformation of the vibrational progression as well as to the splitting of transition energies. Including a realistic Gaussian broadening, good quantitative agreement with the experimental data for refractive index and absorption coefficient is achieved.