title: Separation of dynamic and nondynamic correlation.
abstract: The account of electron correlation and its efficient separation into dynamic and nondynamic parts plays a key role in the development of computational methods. In this paper we suggest a physically-sound matrix formulation to split electron correlation into dynamic and nondynamic parts using the two-particle cumulant matrix and a measure of the deviation from idempotency of the first-order density matrix. These matrices are applied to a two-electron model, giving rise to a simplified electron correlation index that (i) depends only on natural orbitals and their occupancies, (ii) can be straightforwardly decomposed into orbital contributions and (iii) splits into dynamic and nondynamic correlation parts that (iv) admit a local version. These expressions are shown to account for dynamic and nondynamic correlation in a variety of systems containing different electron correlation regimes, thus providing the first separation of dynamic and nondynamic correlation using solely natural orbital occupancies.
authors: Faculty of Chemistry, University of the Basque Country UPV/EHU, and Donostia International Physics Center (DIPC)., P.K. 1072, 20080 Donostia, Euskadi, Spain. eloy.raco@gmail.com ematito@gmail.com and Department of Chemistry, University of California Berkeley, Berkeley, California 94720, USA.
authors: Eloy
authors: E
authors: Ramos-Cordoba
authors: Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, University of Girona, 17071 Girona, Catalonia, Spain.
authors: Pedro
authors: P
authors: Salvador
authors: Faculty of Chemistry, University of the Basque Country UPV/EHU, and Donostia International Physics Center (DIPC)., P.K. 1072, 20080 Donostia, Euskadi, Spain. eloy.raco@gmail.com ematito@gmail.com and IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain.
authors: Eduard
authors: E
authors: Matito