Theoretical study of excitation energy transfer and nonlinear spectroscopy of photosynthetic light-harvesting complexes using the nonperturbative reduced dynamics method

The highly efficient excitation energy transfer (EET) processes in photosynthetic light-harvesting complexes have attracted much recent research interests. Experimentally, spectroscopic studies have provided important information on the energetics and EET dynamics. Theoretically, due to the large number of degrees of freedom and the complex interaction between the pigments and the protein environment, it is impossible to simulate the whole system quantum mechanically. Effective Hamiltonian models are often used, in which the most important degrees of freedom are treated explicitly and all the other degrees of freedom are treated as a thermal bath. However, even with such simplifications, solving the real-time quantum dynamics could still be a difficult task. A particular challenging case in simulating the EET dynamics and related spectroscopic phenomena lies in the so-called intermediate coupling regime, where the intermolecular electronic couplings and the electronic-vibrational couplings are of similar strength. In this article, we review theoretical studies of linear and nonlinear spectroscopic signals of photosynthetic light-harvesting complexes, using the nonperturbative hierarchical equations of motion (HEOM) approach. Simulations were performed for the EET dynamics, various types of linear spectra, two-dimensional electronic spectra, and pump-probe spectra. Benchmark tests of several approximate methods related to the HEOM approach were also discussed. The results show that the nonperturbative HEOM approach is an effective method in simulating the EET dynamics and spectroscopic signals of photosynthetic light-harvesting complexes. Important insights into EET pathways, quantum effects including quantum delocalization, and quantum coherence in photosynthetic light-harvesting complexes were also obtained through such simulations. This article is categorized under: Theoretical and Physical Chemistry > Reaction Dynamics and Kinetics Theoretical and Physical Chemistry > Spectroscopy Software > Simulation Methods

Automated summary

This article reviews theoretical studies of photosynthetic light-harvesting complexes using the nonperturbative hierarchical equations of motion (HEOM) approach to simulate EET dynamics and spectroscopic signals. The results demonstrate the effectiveness of the HEOM method in understanding EET pathways and quantum effects in these complexes through simulations.