Energy transfers between the B850 antennas: hybrid hierarchical equation approach

We model the energy transfers between two B850 antenna units using the hybrid hierarchical equation (HEOM) method, where intra-B850 dynamics is evaluated nonperturbatively using HEOM, whereas inter-B850 transfers are treated by the generalized Förster theory. To account for a conformation-induced energetic disorder we use a realistic model emerging from a quantitative explanation of the single molecule spectral fluctuations in the B850 antenna. The disorder produces a variety of configurations including realizations where the exciton states are predominantly localized at the red-shifted sites. A slow detrapping of excitation from the red states can compete with the transfers to the adjacent B850 unit, thus slowing down the whole equilibration dynamics. In order to highlight the interplay between intra-B850 dynamics and migration to neighboring B850 complex we analyze the diversity of scenarios produced by specific disorder patterns within both donor and acceptor units.