The electronic landscape of the P-cluster of nitrogenase

The electronic structure of the metal cofactors of nitrogenase is central to biological nitrogen fixation. However, the P-cluster and iron molybdenum cofactor, each containing eight metal ions, have long resisted detailed characterization of their low-lying electronic states. Through exhaustive many-electron wavefunction simulation, we report on the full low-energy landscape of the P-cluster in three biologically relevant oxidation states. We trace the origin of the low-lying spectrum to the underlying local atomic states and their global recoupling, and how the interplay between antiferromagnetism, delocalization, and spin frustration as the geometry changes upon oxidation gives rise to the structure of the electronic landscape. Our results support the narrative that many-electron wavefunction simulations stand to provide a resolution of the complicated cofactors in nitrogenase at the electronic level.