arXiv:1001.0110v1 [physics.chem-ph] 31 Dec 2009 On the Dimers of Pseudoisocyanine P.O.J. Scherer ∗ Physics Department T38, TU Munich, 85748 Garching The self organisation of pseudoisocyanine-dimers in dilute aqueous solutions is studied by classical MD simulations. The electronic structure of the dimer is evaluated with the semiempirical ZINDO method to determine the fluctuations of site energies and excitonic coupling. We study different dimer conformations with blue or red shifted absorption maxima as models for H and J-aggregates. The width of the absorption bands is mainly explained by low frequency vibrations whereas the fluctuations of site energies are less important. Abstract 1