{"paper":{"title":"Degenerate coupled-cluster theory","license":"http://arxiv.org/licenses/nonexclusive-distrib/1.0/","headline":"A new coupled-cluster ansatz called ΔCC computes energies and wave functions from any degenerate or nondegenerate Slater-determinant reference while staying size-extensive and converging to full configuration interaction.","cross_cats":["cond-mat.str-el","nucl-th"],"primary_cat":"physics.chem-ph","authors_text":"So Hirata","submitted_at":"2026-01-23T20:49:00Z","abstract_excerpt":"A size-extensive, converging, black-box, ab initio coupled-cluster ($\\Delta$CC) ansatz is introduced that computes the energies and wave functions of stationary states from any degenerate or nondegenerate Slater-determinant references with any numbers of $\\alpha$- and $\\beta$-spin electrons, any patterns of orbital occupancy, any spin multiplicities, and any spatial symmetries. For a nondegenerate reference, it reduces to the single-reference coupled-cluster ansatz. For a degenerate multireference, it is a natural coupled-cluster extension of degenerate Rayleigh-Schr\\\"{o}dinger perturbation ($"},"claims":{"count":4,"items":[{"kind":"strongest_claim","text":"A size-extensive, converging, black-box, ab initio coupled-cluster (ΔCC) ansatz is introduced that computes the energies and wave functions of stationary states from any degenerate or nondegenerate Slater-determinant references with any numbers of α- and β-spin electrons, any patterns of orbital occupancy, any spin multiplicities, and any spatial symmetries.","source":"verdict.strongest_claim","status":"machine_extracted","claim_id":"C1","attestation":"unclaimed"},{"kind":"weakest_assumption","text":"That the newly defined ΔCC ansatz is size-extensive and converges to the full-configuration-interaction limit for arbitrary references and that the slight modification yielding QCC preserves these properties without introducing uncontrolled approximations.","source":"verdict.weakest_assumption","status":"machine_extracted","claim_id":"C2","attestation":"unclaimed"},{"kind":"one_line_summary","text":"A size-extensive, converging, black-box coupled-cluster ansatz (ΔCC) is introduced for arbitrary degenerate or nondegenerate references, reducing to standard CC when appropriate, with a related state-universal QCC variant developed for strong correlation.","source":"verdict.one_line_summary","status":"machine_extracted","claim_id":"C3","attestation":"unclaimed"},{"kind":"headline","text":"A new coupled-cluster ansatz called ΔCC computes energies and wave functions from any degenerate or nondegenerate Slater-determinant reference while staying size-extensive and converging to full configuration interaction.","source":"verdict.pith_extraction.headline","status":"machine_extracted","claim_id":"C4","attestation":"unclaimed"}],"snapshot_sha256":"298a2631e90377309046eb783f15f7e5a4f3b401115f4df7481982165598bdbb"},"source":{"id":"2601.17163","kind":"arxiv","version":4},"verdict":{"id":"f897a2d0-3c79-4051-82ed-ffc0947dd3f3","model_set":{"reader":"grok-4.3"},"created_at":"2026-05-16T11:19:33.802931Z","strongest_claim":"A size-extensive, converging, black-box, ab initio coupled-cluster (ΔCC) ansatz is introduced that computes the energies and wave functions of stationary states from any degenerate or nondegenerate Slater-determinant references with any numbers of α- and β-spin electrons, any patterns of orbital occupancy, any spin multiplicities, and any spatial symmetries.","one_line_summary":"A size-extensive, converging, black-box coupled-cluster ansatz (ΔCC) is introduced for arbitrary degenerate or nondegenerate references, reducing to standard CC when appropriate, with a related state-universal QCC variant developed for strong correlation.","pipeline_version":"pith-pipeline@v0.9.0","weakest_assumption":"That the newly defined ΔCC ansatz is size-extensive and converges to the full-configuration-interaction limit for arbitrary references and that the slight modification yielding QCC preserves these properties without introducing uncontrolled approximations.","pith_extraction_headline":"A new coupled-cluster ansatz called ΔCC computes energies and wave functions from any degenerate or nondegenerate Slater-determinant reference while staying size-extensive and converging to full configuration interaction."},"references":{"count":0,"sample":[],"resolved_work":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57","internal_anchors":0},"formal_canon":{"evidence_count":2,"snapshot_sha256":"dcb678000498b645719c0b8190a57965898e5ea5afedfa6811f48a333e6aa17d"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}