The gain comes from the solver: energy and spin identity in sample-based quantum diagonalization, from N₂ to iron–sulfur clusters

Pre-print. Sample-based quantum diagonalization (SQD) on N₂ and two iron–sulfur clusters, [2Fe-2S] and [4Fe-4S]: a combined loop on IBM quantum processors that aims each circuit from the loop’s current eigenvector, a determinant-level solver with a spin penalty seeded from the quantum determinants, orbital optimization, and an exact N₂ window, each with its classical control; the energy is reported with ⟨S²⟩. Replication package: 10.5281/zenodo.23705888. Files restricted during review.