Mortaza Aghtar

• Efficient energy transfer in photosynthetic organisms is a known phenomenon since decades but some of its details are still unknown. Observation of quantum coherence in the light-harvesting complex (LHC) of photosynthetic systems has boosted interest in this field to explore this quantum behaviour as a candidate for this high efficiency. We used a semi-classical wave-packet dynamics approach to investigate the influence of environmental vibrations on the excitation energy transfer (EET) among the pigments of LHCs. In this method, a QM/MM approach on a classical molecular dynamics trajectory was employed to calculate the excitation energies and couplings to build the excitonic Hamiltonian. The method was validated with an exact density matrix approach using a two-level system model. Subsequently, the method was applied to investigate the EET in Fenna-Mathews-Olson (FMO) complex, the LHC of green sulphur bacteria, and the Pycoerythrin 545 (PE 545) antenna aggregate in marine algae. We have shown that the pigments in the FMO and PE 545 complexes are coupled to their respective environments with a similar coupling strength. The coupling stems, however, from different origins, i.e. intramolecular vibrations or environmental ones.