{
  "abstract": "We introduce NOCI-RSPT, a framework for constructing perturb-then-diagonalize multireference perturbation theories for model spaces defined by nonorthogonal determinants. NOCI-RSPT realizes order-by-order size consistency by orthogonalizing the effective Hamiltonian before perturbatively truncating it and removes problematic internal excitations through model-space projection. The resulting second- and third-order theories, NOCI-RS2 and NOCI-RS3, recover MP2 and MP3 in the single-reference limit and exhibit the same respective cost scaling at fixed model-space size. Calculations on assemblies of multireference $\\mathrm{H}_2$ fragments demonstrate size consistency, while calculations of the low-energy states of $\\mathrm{H}_2$ along its dissociation curve demonstrate improved numerical stability and characterize the influence of intruder states. The latter calculations demonstrate the exceptional accuracy achieved by NOCI-RS3 and illustrate how model-space expansion and amplitude regularization can mitigate the effects of large perturbative corrections. Altogether, NOCI-RSPT provides a systematic route to low-scaling multireference perturbation theories built from single-reference methods.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2611.07244",
  "author_total": 3,
  "authors": [
    {
      "name": "Alex Krotz"
    },
    {
      "name": "K. Birgitta Whaley"
    },
    {
      "name": "Martin Head-Gordon"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/8vrrs6rb63ech.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2611.07244",
  "fulltext_url": null,
  "id": "8vrrs6rb63ech",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2611.07244",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "physics.chem-ph"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2611.07244",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-04",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/8vrrs6rb63ech.ris",
  "sources": [
    {
      "first_seen": "2026-11-06T18:21:30Z",
      "native_id": "2611.07244",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2611.07244"
    }
  ],
  "subjects": [
    {
      "field": "chemistry",
      "origin": "arxiv:physics.chem-ph",
      "subfield": "physical"
    }
  ],
  "title": "Multireference perturbation theory with nonorthogonal determinants",
  "title_text": "Multireference perturbation theory with nonorthogonal determinants",
  "type": "preprint",
  "updated_at": "2026-11-09T00:20:40Z",
  "url": "https://research.draconitic.com/paper/8vrrs6rb63ech",
  "venue": "arXiv",
  "versions": []
}