{
  "abstract": "Core-to-valence transitions are sensitive probes of unoccupied valence orbitals and are especially informative for open-shell molecules and materials, where frontier molecular orbitals are often degenerate or nearly so. Accurate simulation of core-level spectra for open-shell molecules is challenging because methods such as time-dependent density functional theory (TDDFT) typically rely on a spin-unrestricted reference determinant, leading to spin contamination. A restricted open-shell reference state eliminates spin contamination in the ground state but excited states computed using the configuration-interaction singles (CIS) approach may yet exhibit significant spin contamination. This can be eliminated by extending the CIS excitation space to include a small number of doubly substituted determinants, in what has been called “extended” (X)CIS, and this approach affords a variational and size-consistent wave function for each excited state, free of spin contamination but also free of dynamical correlation. Here, we introduce the latter via density functional theory (DFT), using Kohn-Sham orbitals within the XCIS formalism and scaling the electron repulsion integrals to reduce double-counting of correlation effects. Reasonable valence excitation energies are obtained with the new DFT/XCIS approach, and combing it with core/valence separation (DFT/ XCIS-CVS) extends the method to core-level spectroscopy. Absolute excitation energies for K-edge transitions are improved, relative to conventional TDDFT, by means of an empirical shift in the 1s eigenvalues. Incorporation of dynamical correlation improves the accuracy of spectral splittings for open-shell systems, relative to the recently reported XCIS-CVS approach.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": null,
  "author_total": 2,
  "authors": [
    {
      "name": "Avik Kumar Ojha"
    },
    {
      "name": "John M. Herbert",
      "orcid": "0000-0002-1663-2278"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/3grx1gq2djnvq.bib",
  "cited_by": 0,
  "doi": "10.26434/chemrxiv.15008165/v1",
  "fulltext_url": null,
  "id": "3grx1gq2djnvq",
  "issns": [],
  "landing_url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008165/v1",
  "language": null,
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "journal",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "3107|Advanced Chemical Physics Studies"
    ]
  ],
  "openalex": "W7204934113",
  "pdf_url": "https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.15008165/v1",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-01",
  "publisher": "American Chemical Society (ACS)",
  "ris": "https://research.draconitic.com/paper/3grx1gq2djnvq.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:17Z",
      "native_id": "10.26434/chemrxiv.15008165",
      "source": "chemrxiv",
      "url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008165/v1"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "openalex:3107|Advanced Chemical Physics Studies",
      "subfield": "amo"
    }
  ],
  "title": "DFT/XCIS: A Kohn-Sham Approach to Extended Configuration-Interaction Singles, for Valence- and Core-Level Spectroscopy of Open-Shell Systems",
  "title_text": "DFT/XCIS: A Kohn-Sham Approach to Extended Configuration-Interaction Singles, for Valence- and Core-Level Spectroscopy of Open-Shell Systems",
  "type": "preprint",
  "updated_at": "2026-10-30T12:17:17Z",
  "url": "https://research.draconitic.com/paper/3grx1gq2djnvq",
  "venue": "ChemRxiv",
  "versions": []
}