Successes, challenges, and opportunities for quantum chemistry in understanding metalloenzymes for solar fuels research.

Quantum chemical approaches today are a powerful tool to study the properties and reactivity of metalloenzymes. In the field of solar fuels research these involve predominantly photosystem II and hydrogenases, which catalyze water oxidation and hydrogen evolution, as well as related biomimetic and bio-inspired models. Theoretical methods are extensively used to better comprehend the nature of catalytic intermediates, establish important structure-function and structure-property correlations, elucidate functional principles, and uncover the catalytic activity of these complex systems by unravelling the key steps of their reaction mechanism. Computations in the field of water oxidation and hydrogen evolution are used as predictive tools to elucidate structures, explain and synthesize complex experimental observations from advanced spectroscopic techniques, rationalize reactivity on the basis of atomistic models and electronic structure, and guide the design of new synthetic targets. This feature article covers recent advances in the application of quantum chemical methods for understanding the nature of catalytic intermediates and the mechanism by which photosystem II and hydrogenases achieve their function, and points at essential questions that remain only partly answered and at challenges that will have to be met by future advances and applications of quantum and computational chemistry.