Optical spectroscopy and system bath interactions in molecular aggregates with full configuration interaction Frenkel exciton model
Abstract Standard application of the Frenkel exciton model neglects resonance coupling between collective molecular aggregate states with different number of excitations. These inter band coupling terms are, however, of the same magnitude as the intra band coupling between singly excited states. We systematically derive the Frenkel exciton model from quantum chemical considerations, and identify it as a variant of the configuration interaction method. We discuss all non negligible couplings between collective aggregate states, and provide compact formulae for their calculation. We calculate absorption spectra of molecular aggregate of carotenoids and identify significant band shifts as a result of inter band coupling. The presence of inter band coupling terms requires renormalization of the system bath coupling with respect to standard formulation, but renormalization effects are found to be weak. We present detailed discussion of molecular dimer and calculate its time resolved two dimensional Fourier transformed spectra to find weak but noticeable effects of peak amplitude redistribution due to inter band coupling.