{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T02:36:16Z","timestamp":1760236576993,"version":"build-2065373602"},"reference-count":49,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2021,12,9]],"date-time":"2021-12-09T00:00:00Z","timestamp":1639008000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"HPC-EUROPA3","award":["INFRAIA-2016-1- 730897"],"award-info":[{"award-number":["INFRAIA-2016-1- 730897"]}]},{"DOI":"10.13039\/501100007514","name":"University of Pisa","doi-asserted-by":"publisher","award":["Fondi di Ateneo"],"award-info":[{"award-number":["Fondi di Ateneo"]}],"id":[{"id":"10.13039\/501100007514","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Computation"],"abstract":"<jats:p>In this work, we present a method to build a first order reduced density matrix (1-RDM) of a molecule from variational Quantum Monte Carlo (VMC) computations by means of a given correlated mapping wave function. Such a wave function is modeled on a Generalized Valence Bond plus Complete Active Space Configuration Interaction form and fits at best the density resulting from the Slater-Jastrow wave function of VMC. The accuracy of the method proposed has been proved by comparing the resulting kinetic energy with the corresponding VMC value. This 1-RDM is used to analyze the amount of correlation eventually captured in Kohn-Sham calculations performed in an unrestricted approach (UKS-DFT) and with different energy functionals. We performed test calculations on a selected set of molecules that show a significant multireference character. In this analysis, we compared both local and global indicators of nondynamic and dynamic correlation. Moreover, following the natural orbital decomposition of the 1-RDM, we also compared the effective temperatures of the corresponding Fermi-like distributions. Although there is a general agreement between UKS-DFT and VMC, we found the best match with the functional LC-BLYP.<\/jats:p>","DOI":"10.3390\/computation9120135","type":"journal-article","created":{"date-parts":[[2021,12,9]],"date-time":"2021-12-09T21:52:32Z","timestamp":1639086752000},"page":"135","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Extraction of a One-Particle Reduced Density Matrix from a Quantum Monte Carlo Electronic Density: A New Tool for Studying Nondynamic Correlation"],"prefix":"10.3390","volume":"9","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-7320-3421","authenticated-orcid":false,"given":"Carmelo","family":"Naim","sequence":"first","affiliation":[{"name":"Institut des Sciences Mol\u00e9culaires (ISM, UMR CNRS 5255), University of Bordeaux, 351 Cours de la Lib\u00e9ration, 33405 Talence, France"},{"name":"Dipartimento di Chimica e Chimica Industriale, Universit\u00e0 di Pisa, Via Giuseppe Moruzzi 13, I-56124 Pisa, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8024-6972","authenticated-orcid":false,"given":"Claudio","family":"Amovilli","sequence":"additional","affiliation":[{"name":"Dipartimento di Chimica e Chimica Industriale, Universit\u00e0 di Pisa, Via Giuseppe Moruzzi 13, I-56124 Pisa, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2021,12,9]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1509","DOI":"10.1103\/PhysRev.97.1509","article-title":"Quantum Theory of Many-Particle Systems. 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