Limits and potentials of quantum chemical methods in modelling photosynthetic antennae

Abstract

Advances in electronic spectroscopies with femtosecond time resolution have provided new information on the excitonic processes taking place during the energy conversion in natural photosynthetic antennae. This has promoted the development of new theoretical protocols aiming at accurately describing the properties and mechanisms of exciton formation and relaxation. In this perspective, we provide an overview of the quantum chemical based approaches, trying to underline both the potentials of the methods and their weaknesses. In particular three main aspects will be analysed, the quantum mechanical description of excitonic parameters (site energies and couplings), the incorporation of environmental effects on these parameters through hybrid quantum/classical approaches, and the modelling of the dynamical coupling among such parameters and the vibrations of the pigment-protein complex.

Open quantum system parameters for light harvesting complexes from molecular dynamics

“…5 and 6. This method has been applied in recent years to various light harvesting complexes. [1][2][3][4][5][6][7][8][9][10][11][12][13] The electronic system Hamiltonians extracted from these calculations typically agree reasonably well with those extracted from fitting simple exciton models to experimental spectra. However, they show a large spread in parameters, even the energetic ordering of the site energies is not agreed upon by all calculations.…”

Benchmarking Calculations of Excitonic Couplings between Bacteriochlorophylls

“…However, the electronic properties of chlorophyll molecules are known to vary substantially with the molecular geometry [37][38][39]. To test the influence of geometry optimization on BChl couplings, we compared the electronic-structure results obtained with different geometry optimizations and with experiment.…”

Macrocycle ring deformation as the secondary design principle for light-harvesting complexes

“…In any case, a full understanding of the energy transfer process is only possible with a correct description of the interaction between the chromophores and their fluctuating protein environment. A lot of effort has been devoted to this subject recently (7)(8)(9)(10)(11)(12)(13)(14)(15)(16). The environment affects both site energies and couplings and is a constant source of noise; this has a smearing effect on experimental spectra and poses great challenges to theoretical treatments.…”