Developments for the theoretical description of X-ray spectroscopy of multinuclear catalysts and metalloproteins.

Oxygen evolution and nitrogen fixation are some of the most important chemical reactions, both in biology and in our society.

As multinuclear transition metal complexes are the types of catalysts Nature chose to perform these reactions, they have been the focus of a lot of research.

Yet, the chemistry of these multinuclear transition metal complexes is still not well understood.X-ray spectroscopy has unique properties that makes it a very attractive method to study these complexes and provide crucial and detailed information on the local electronic structure.

However, accurate and predictive theoretical models are needed to extract this information and convert it into chemical insight.One family of theoretical methods that has recently gained traction for this purpose is multi-configurational methods.

These are particularly adapted to simulate molecules with complicated electronic structures, such as transition metal complexes and excited states.

However, their high cost has restricted their application and in particular currently prevents the calculation of multinuclear complexes.In this project, we suggest combining together for the first time three modern techniques to address this issue.

This new paradigm promises to be several orders of magnitude more efficient than the current multiconfigurational methods, opening up the possibility to investigate a significantly wider range of complexes that were so-far out of reach for theory.