Excitation dynamics in B800-B850 antenna: hierarchical equation versus perturbative approaches

We verify various perturbative methods frequently used for modeling of the excitation dynamics within photosynthetic LH2 (B800-B850) antenna by comparing them with an exact (nonperturbative) hierarchical equation (HEOM) approach. We have found that secular theories (like coherent modified Redfield, and combined Redfield-Förster approaches) fail to describe the dynamics, giving too fast transfers within the B800 and B850 bands and too fast B800→B850 conversion due to the neglect of the population-to-coherence transfers. On the other hand, the standard Redfield theory with the full relaxation tensor is capable to give a quantitatively correct picture consistent with the HEOM solution (with an accuracy of some deviations from the exact kinetics due to absence of dynamic localization associated with the B800→B850 pathways). Being computationally inexpensive this theory can be used for modeling of linear and nonlinear spectral responses of various LH2 complexes with averaging over energetic disorder in the cases when the use of nonperturbative methods is limited due to their numerical complexity.