Quantum Chemical Description of Absorption Properties and Excited‐State Processes in Photosynthetic Systems

Abstract

The theoretical description of the initial steps in photosynthesis has gained increasing importance over the past few years. This is caused by more and more structural data becoming available for light-harvesting complexes and reaction centers which form the basis for atomistic calculations and by the progress made in the development of first-principles methods for excited electronic states of large molecules. In this Review, we discuss the advantages and pitfalls of theoretical methods applicable to photosynthetic pigments. Besides methodological aspects of excited-state electronic-structure methods, studies on chlorophyll-type and carotenoid-like molecules are discussed. We also address the concepts of exciton coupling and excitation-energy transfer (EET) and compare the different theoretical methods for the calculation of EET coupling constants. Applications to photosynthetic light-harvesting complexes and reaction centers based on such models are also analyzed.

Influence of Force Fields and Quantum Chemistry Approach on Spectral Densities of BChl a in Solution and in FMO Proteins

“…On the other hand, quantum chemistry calculations for these complexes are still very expensive especially if one wants to combine them with timedependent calculations. 19 Therefore, a sequential coupling of MD calculations, QM/MM (quantum mechanics/molecular mechanics), and quantum dynamical simulations has been proposed. 20 One of the key properties being calculated in this and similar schemes is the spectral density which determines the frequency-dependent coupling between relevant system degrees of freedom and thermal bath modes.…”

Singlet fission in carotenoid aggregates: insights from transient absorption spectroscopy

“…The electronic interaction between chromophores (exciton coupling) is crucial for energy transfer in photosynthesis. [5][6][7][8][9] The exciton coupling between carotenoids has also been proposed as an explanation for unique colors in flower petals 10 and the shells of crustaceans. 11,12 One photophysical mechanism that fundamentally depends upon electronic coupling between chromophores is singlet fission.…”

The Unique Photophysical Properties of the Peridinin-Chlorophyll-a-Protein

“…TD-DFT methods agree that the molecular motion can be responsible of the inversion between states. From a methodological point of view TD-DFT is known to reverse the A g - B u + order [43] and some agreement is obtained by employing Tamm-Dancoff approximation even if this can be considered fortuitous [26]. Semi-empirical, MNDO-PSDCI methods are in good agreement with experiments [25, 32, 44, 45] as well as EOM-CCSD methods [17, 32] even if the doubly excited dark state, A g - , can be poorly described by these last methods as suggested by Krylov [46].…”