Nature is extremely efficient in harvesting sunlight via fascinating supramolecular structures, with the light-harvesting apparatus of purple bacteria providing beautiful examples. Density Functional Theory (DFT) and its time-dependent extension offer the unique chance to unravel the pathways of energy- and charge transfer in these systems, but are challenged by the complexity of the underlying electronic structure problem. Local and semi local functionals, such as the Local Density Approximation and Generalized Gradient Approximations (GGAs), offer the computational efficiency for studying systems of the relevant size. They fail, however, in describing long-range charge-transfer processes correctly. The latter can be reliably computed with exact-exchange based range-separated hybrids, but these are computationally too expensive for studying the light harvesting apparatus. A DFT-based understanding how nature has solved its energy problem is therefore tied to improving the accuracy of semi local functionals. Newly developed Meta-GGAs are able to capture non-local response properties of exact exchange. We will discuss this development and put it in connection with the light-harvesting question.

Dreaming of banishing exact exchange: Semi local functionals as a key to understanding natural light harvesting?

255th National Meeting (2018)

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