{
  "abstract": "Under the assumption that the static correlation can well be described by selected configuration interaction, to the extent that the residual dynamic correlation can be accounted for accurately by a second-order perturbation theory (PT2), a family of multireference PT2s (iCI-MRPT2) based on the iterative configuration interaction with selection are proposed and compared. The first step is to partition a large complete active space (CAS) $P$ into the direct sum of a primary ($P_m$) and a secondary ($P_s$) subspace via a parameter $C_{\\mathrm{min}}$. The former serves as the actual reference space, whereas the latter is treated via Epstein-Nesbet PT2. An MRPT2 is then invoked to account for the dynamic correction of the $Q=1-P$ space to the $P_m$ space. Different MRPT2s are distinguished by the underlying zeroth-order Hamiltonians. To circumvent the prohibitive computational cost and memory footprint associated with high-order reduced density matrices in the fully internally contracted scheme and the exponential growth of external functions (XF) in the uncontracted scheme, a partial contraction strategy is employed for constructing the XFs: those involving one or two inactive (core or virtual) orbitals are kept uncontracted, whereas those involving three or four inactive orbitals are internally contracted. They span the uncontracted ($Q_u$) and contracted ($Q_c$) portions of $Q$, respectively. The former is further split into two subspaces $Q_u^c$ and $Q_u^u$ via a parameter $Q_{\\mathrm{min}}$, which are to be treated in coupled and uncoupled manners, respectively. Extrapolations to zero $Q_{\\mathrm{min}}$ and $C_{\\mathrm{min}}$ can be performed, so as to approach CAS-based MRPT2. Calculations with active spaces as large as CAS(56e,58o) can now be performed. The size-consistency of the iCI-MRPT2s is also analyzed in detail.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.37221",
  "author_total": 2,
  "authors": [
    {
      "name": "Ning Zhang"
    },
    {
      "name": "Wenjian Liu"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/4cf79jhms0xn5.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.37221",
  "fulltext_url": null,
  "id": "4cf79jhms0xn5",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.37221",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "physics.chem-ph"
    ],
    [
      "openalex",
      "3107|Advanced Chemical Physics Studies"
    ]
  ],
  "openalex": "W7224116242",
  "pdf_url": "https://arxiv.org/pdf/2610.37221",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-27",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/4cf79jhms0xn5.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:35:50Z",
      "native_id": "2610.37221",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.37221"
    }
  ],
  "subjects": [
    {
      "field": "chemistry",
      "origin": "arxiv:physics.chem-ph",
      "subfield": "physical"
    }
  ],
  "title": "Multireference Second-Order Perturbation Theories Based on Iterative Configuration Interaction with Selection",
  "title_text": "Multireference Second-Order Perturbation Theories Based on Iterative Configuration Interaction with Selection",
  "type": "preprint",
  "updated_at": "2026-10-30T12:35:50Z",
  "url": "https://research.draconitic.com/paper/4cf79jhms0xn5",
  "venue": "arXiv",
  "versions": []
}