{"about":{"site":"https://codewithpapers.app","non_affiliation":"Code with Papers and Syntology are not affiliated with, endorsed by, or sponsored by Papers with Code, Meta, or the pwc-archive mirror.","licence":"CC BY-SA 4.0","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","attribution":"https://codewithpapers.app/attribution","modified":"archive material modified by Syntology; see the attribution page"},"url":"/paper/state-specific-coupled-cluster-methods-for","title":"State-Specific Coupled-Cluster Methods for Excited States","arxiv_id":"2401.05048","date":"2024-01-10","proceeding":null,"authors":["Yann Damour","Anthony Scemama","Denis Jacquemin","Fábris Kossoski","Pierre-François Loos"],"abstract":"We reexamine $\\Delta$CCSD, a state-specific coupled-cluster (CC) with single and double excitations (CCSD) approach that targets excited states through the utilization of non-Aufbau determinants. This methodology is particularly efficient when dealing with doubly excited states, a domain where the standard equation-of-motion CCSD (EOM-CCSD) formalism falls short. Our goal here is to evaluate the effectiveness of $\\Delta$CCSD when applied to other types of excited states, comparing its consistency and accuracy with EOM-CCSD. To this end, we report a benchmark on excitation energies computed with the $\\Delta$CCSD and EOM-CCSD methods, for a set of molecular excited-state energies that encompasses not only doubly excited states but also doublet-doublet transitions and (singlet and triplet) singly-excited states of closed-shell systems. In the latter case, we rely on a minimalist version of multireference CC known as the two-determinant CCSD method to compute the excited states. Our dataset, consisting of 276 excited states stemming from the \\textsc{quest} database [V\\'eril \\textit{et al.}, \\textit{WIREs Comput. Mol. Sci.} \\textbf{2021}, 11, e1517], provides a significant base to draw general conclusions concerning the accuracy of $\\Delta$CCSD. Except for the doubly-excited states, we found that $\\Delta$CCSD underperforms EOM-CCSD. For doublet-doublet transitions, the difference between the mean absolute errors (MAEs) of the two methodologies (of \\SI{0.10}{\\eV} and \\SI{0.07}{\\eV}) is less pronounced than that obtained for singly-excited states of closed-shell systems (MAEs of \\SI{0.15}{\\eV} and \\SI{0.08}{\\eV}). This discrepancy is largely attributed to a greater number of excited states in the latter set exhibiting multiconfigurational characters, which are more challenging for $\\Delta$CCSD.","url_abs":"https://arxiv.org/abs/2401.05048v2","url_pdf":"https://arxiv.org/pdf/2401.05048v2.pdf","source":{"archive":"pwc-archive (Hugging Face), CC BY-SA 4.0","snapshot":"2025-07-28","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","row_kind":"links_only","authors_date_abstract":"arXiv metadata, CC0 1.0 (https://info.arxiv.org/help/license), from the Kaggle arXiv metadata snapshot of 2026-09-12"},"code_links":[{"paper_slug":"state-specific-coupled-cluster-methods-for","repo_url":"https://github.com/lcpq/simplewick","is_official":1,"mentioned_in_paper":1,"mentioned_in_github":0,"framework":"none","reach":null}],"tasks":[],"methods":[],"datasets_introduced":[],"methods_introduced":[],"results":[],"syntology":{"atlas_url":null,"mcp":null,"developers":"https://syntology.ai/developers"},"arxiv_metadata":null,"syntology_extracted_results":null}