{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"aca5e3f22777fca19f85316e42ac56b37916d0937a2f99eef066c0d560f74685","created":"2026-10-03T07:17:58Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"31bd9167c638af39c71710b429089a4a38d9a3c62e2098c95169cdf100a67b06","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"chem.strong-correlation.femoco-ground-state","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"FeMoco is the cluster of seven iron atoms and one molybdenum atom in the enzyme that turns nitrogen from air into ammonia. Nobody has computed reliably which arrangement of electron spins and charges it adopts in its resting state.","posed_since":"","precise":"For the resting state $E0$ of FeMoco (MoFe7S9C cluster with homocitrate, total spin $S = 3/2$), determine the Fe oxidation-state distribution consistent with Mo(III), the spin-coupling pattern of the eight metal spins and the ordering of the lowest spin states, with energies converged to $1\\,\\mathrm{kcal}/\\mathrm{mol}$ in an active space large enough that the answer no longer changes with its size. An answer is a converged wavefunction calculation (or set of agreeing methods) that also reproduces measured Mossbauer, EPR and X-ray spectroscopic data.","problem_ref":null,"references":"","settled_by":"Converged many-electron calculations in a systematically enlarged active space, embedded in the protein, that agree with each other and with the measured spectroscopic parameters.","status_note":"X-ray spectroscopy in 2014 (Bjornsson et al., Chem. Sci., https://doi.org/10.1039/c4sc00337c) identified a spin-coupled Mo(III), and a [MoFe7S9C]^1- charge state is favored; the Fe valence distribution, the spin-coupling pattern and converged spin-state energetics remain open.","title":"Electronic ground state of the nitrogenase FeMo 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