Environmental effects on the dynamics in the light-harvesting complexes LH2 and LH3 based on molecular simulations

Although a multitude of theoretical studies exist on light-harvesting complex 2 (LH2), less is known about the light-harvesting complex 3 (LH3) of similar ring-like structure. In a comparative study of three system, i.e., the LH2 protein-pigment aggregate of the purple bacterium Rhodospirillum molischianum as well as for the LH2 and LH3 complexes of Rhodoblastus acidophilus the similarities and the differences in the excitonic system were analyzed. To this end, the systems have been studied in a multi-scale approach that combines molecular dynamics simulations with quantum chemistry calculations and quantum dynamics. Along the ground-state molecular dynamics trajectories, the excited energy gaps were determined in a quantum mechanics/molecular mechanics hybrid fashion. Based on the simulations, spectral densities, absorption spectra and exciton dynamics have been determined. After correcting for some shortcoming in the absorption spectra, the exciton dynamics within and between the ring systems have been determined and discussed.