ИСТИНА

Theoretical description of pigment­pigment and pigment­protein interaction is a question of a high importance for the understanding of high efficiency of the photosynthetic processes. Pigment-pigment interaction in the supramolecular chromophore­protein complexes provide an effective light absorption and selective interaction with the protein environment ensures excitation energy transfer to the reaction centers where charge separation process occurs. In the current work we report the calculation of spectral properties of circular LH1­RC complexes of purple bacteria Thermochromatium tepidum and rates of excitation energy transfer and excitonic relaxation. To calculate stationary spectra we use method of excitonic Hamiltonians with transition energies calculated by CASSCF/XMCQDPT2 method and excitonic couplings calculated by TrCAMM decomposition. To take into account the site heterogeneity we carried out a separate calculation for each of the bacteriochlorophyll. Calculated absorption, circular dichroism and magnetic circular dichroism spectra agree well with the experimental ones. For the absorption and CD spectra lines of the transition to each excitonic state were non­empirically broadened taking into account electron­phonon interaction with the protein environment. We used conventional approach in which system separated on quantum subsystem (chromophores) and thermal bath (protein). Hamiltonian of system­bath interaction was constructed based on the excitonic wavefunctions of bacteriochlorophyll system and normal modes of the protein. The calculated spectral function of system­bath interaction was used for the calculation of dynamics of excitation energy transfer and excitonic states population. We used a theory of quantum dissipative dynamics with non­equilibrium thermal bath which was previously applied by our group to the process of primary charge separation in the reaction center of Rba. sphaeroides.