  The self organization 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.
