In photosynthetic apparatus of green sulfur bacteria, the Fenna-Matthews-Olson (FMO) complex is responsible for the energy transfer from chlorosomes within the main light harvesting antennae to the reaction center. The proper prediction of spectroscopic signatures of FMO complex, such as absorption and circular dichroism spectra, requires accurate electronic Hamiltonian describing Foster resonance energy transfer (FRET) between the bacteriochlorophyll (BChl) centers of the complex. In this work we propose the new electronic Hamiltonian that was acquired using accurate fragment molecular orbital (fmo) method. The fragment nature of the fmo method allows us to separate the electronic density of entire system into the electronic densities of individual chromophores and their environment. This density separation significantly reduces the computational cost of the FMO complex simulations and provides means for fully quantum mechanical treatment of the system. In addition to reduction of computational cost the density separation gives us ability to predict the direction of the energy transfer between the chromophores as well as the influence of protein environment on FRET between the BChl centers. We also compare the results of the fmo method calculations to the results obtained with hybrid quantum mechanical/molecular mechanical calculations and effective fragment potential calculations. This comparison shows that the different treatment of the protein environment around the chromophores influences the resulting Hamiltonian, highlighting the importance of fully quantum mechanical description of FMO complex.

In search of the new Hamiltonian: Fragment molecular orbital study of Förster resonance energy transfer between bacteriochlorophylls of Fenna-Matthews-Olson complex

256th National Meeting (2018)

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