Thermophysical Properties of Alkali Metals: A Partition Function Theory Approach Including Low-Lying Electronic States

Thermophysical Properties of Alkali Metals: A Partition Function Theory Approach Including Low-Lying Electronic States | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Thermophysical Properties of Alkali Metals: A Partition Function Theory Approach Including Low-Lying Electronic States Carlos D. da Silva, Marcos D. S. Alves, Ramon S. da Silva, Maikel Y. Ballester This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7046161/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 19 Aug, 2025 Read the published version in International Journal of Thermophysics → Version 1 posted 9 You are reading this latest preprint version Abstract A deep understanding of thermophysical properties is crucial for accurately predicting the behavior of molecules under extreme conditions. In this work, we present a comprehensive methodology grounded in statistical mechanics, which integrates quantum, semiclassical, and classical formulations of the partition function for diatomic species. As a case study, this methodology was applied to homonuclear alkali metal dimers through the fitting of high-level ab initio calculations to the Extended Hartree-Fock Approximate Correlation Energy. A total of 154 potential energy curves were considered, with explicit consideration of low-lying electronic states This approach enables accurate modeling of both low and high-temperature regimes for \(\rm Li_{2}\) , \(\rm Na_{2}\) , \(\rm K_{2}\) , \(\rm Rb_{2}\) , \(\rm Cs_{2}\) and \(\rm Fr_{2}\) . Our results reveal that neglecting excited electronic states leads to significant deviations in key properties, particularly heat capacity and enthalpy at elevated temperatures. Systematic trends along the alkali metal series are observed. The methodology demonstrates agreement with experimental data and underscores the limitations of classical approaches, where the quantized nature of molecular eigenvalue becomes non-negligible. This framework provides a robust and generalizable tool for reliable prediction of thermodynamic properties in molecular systems, the results emphasize the fundamental role of electronic structure in determining thermodynamic properties, and they can be directly extended to improve high-temperature models in chemical kinetics, plasma physics, and materials science. Alkali Metal Potential Energy Curve Partition Function Thermophysical Properties Full Text Additional Declarations No competing interests reported. Supplementary Files SupplementaryMaterialThermophysicsAlkaliMetals2025Carlos.pdf CoefficientsEHFACEhomonucleares.ods Cite Share Download PDF Status: Published Journal Publication published 19 Aug, 2025 Read the published version in International Journal of Thermophysics → Version 1 posted Editorial decision: Revision requested 03 Aug, 2025 Reviews received at journal 03 Aug, 2025 Reviewers agreed at journal 03 Aug, 2025 Reviews received at journal 24 Jul, 2025 Reviewers agreed at journal 07 Jul, 2025 Reviewers invited by journal 06 Jul, 2025 Editor assigned by journal 04 Jul, 2025 Submission checks completed at journal 04 Jul, 2025 First submitted to journal 04 Jul, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7046161","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":481312394,"identity":"34065cae-0e7a-4ed7-8292-a7fb75e8384e","order_by":0,"name":"Carlos D. da Silva","email":"","orcid":"","institution":"Universidade Federal de Juiz de Fora","correspondingAuthor":false,"prefix":"","firstName":"Carlos","middleName":"D. da","lastName":"Silva","suffix":""},{"id":481312395,"identity":"71f94b5c-66b5-4669-90f4-4fcfbe22a5b8","order_by":1,"name":"Marcos D. S. 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In this work, we present a comprehensive methodology grounded in statistical mechanics, which integrates quantum, semiclassical, and classical formulations of the partition function for diatomic species. As a case study, this methodology was applied to homonuclear alkali metal dimers through the fitting of high-level ab initio calculations to the Extended Hartree-Fock Approximate Correlation Energy. A total of 154 potential energy curves were considered, with explicit consideration of low-lying electronic states This approach enables accurate modeling of both low and high-temperature regimes for \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\rm Li_{2}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\rm Na_{2}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\rm K_{2}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\rm Rb_{2}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\rm Cs_{2}\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\rm Fr_{2}\\)\u003c/span\u003e\u003c/span\u003e. Our results reveal that neglecting excited electronic states leads to significant deviations in key properties, particularly heat capacity and enthalpy at elevated temperatures. Systematic trends along the alkali metal series are observed. The methodology demonstrates agreement with experimental data and underscores the limitations of classical approaches, where the quantized nature of molecular eigenvalue becomes non-negligible. This framework provides a robust and generalizable tool for reliable prediction of thermodynamic properties in molecular systems, the results emphasize the fundamental role of electronic structure in determining thermodynamic properties, and they can be directly extended to improve high-temperature models in chemical kinetics, plasma physics, and materials science.\u003c/p\u003e","manuscriptTitle":"Thermophysical Properties of Alkali Metals: A Partition Function Theory Approach Including Low-Lying Electronic States","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-07 04:08:55","doi":"10.21203/rs.3.rs-7046161/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-03T11:04:52+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-03T11:03:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"317749139153796084352559924335367340207","date":"2025-08-03T11:02:20+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-24T10:41:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"304155829662134482897535973334341459619","date":"2025-07-07T10:08:42+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-06T15:23:28+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-05T01:44:02+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-05T01:43:26+00:00","index":"","fulltext":""},{"type":"submitted","content":"International Journal of Thermophysics","date":"2025-07-04T11:06:01+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"international-journal-of-thermophysics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ijot","sideBox":"Learn more about [International Journal of Thermophysics](http://link.springer.com/journal/10765)","snPcode":"10765","submissionUrl":"https://submission.nature.com/new-submission/10765/3","title":"International Journal of Thermophysics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"d586ed26-6484-4e9c-9327-b7e7f1acae8b","owner":[],"postedDate":"July 7th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-08-25T16:35:06+00:00","versionOfRecord":{"articleIdentity":"rs-7046161","link":"https://doi.org/10.1007/s10765-025-03628-z","journal":{"identity":"international-journal-of-thermophysics","isVorOnly":false,"title":"International Journal of Thermophysics"},"publishedOn":"2025-08-19 16:29:24","publishedOnDateReadable":"August 19th, 2025"},"versionCreatedAt":"2025-07-07 04:08:55","video":"","vorDoi":"10.1007/s10765-025-03628-z","vorDoiUrl":"https://doi.org/10.1007/s10765-025-03628-z","workflowStages":[]},"version":"v1","identity":"rs-7046161","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7046161","identity":"rs-7046161","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}