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Ghent University Ghent University Academic Bibliography2000-01-01T00:00+00:001dailyVariational optimization of the second-order density matrix corresponding to a seniority-zero configuration interaction wave function
https://biblio.ugent.be/publication/6953981
Poelmans, WardVan Raemdonck, MarioVerstichel, BrechtDe Baerdemacker, StijnTorre, AliciaLain, LuisMassaccesi, Gustavo EAlcoba, Diego RBultinck, PatrickVan Neck, Dimitri2015We perform a direct variational determination of the secondorder (two-particle) density matrix corresponding to a many-electron system, under a restricted set of the two-index N-representability P-, Q-, and G-conditions. In addition, we impose a set of necessary constraints that the two-particle density matrix must be derivable from a doubly occupied manyelectron wave function, i.e., a singlet wave function for which the Slater determinant decomposition only contains determinants in which spatial orbitals are doubly occupied. We rederive the two-index N-representability conditions first found by Weinhold and Wilson and apply them to various benchmark systems (linear hydrogen chains, He, N-2, and CN-). This work is motivated by the fact that a doubly occupied many-electron wave function captures in many cases the bulk of the static correlation. Compared to the general case, the structure of doubly occupied two-particle density matrices causes the associate semidefinite program to have a very favorable scaling as L-3, where L is the number of spatial orbitals. Since the doubly occupied Hilbert space depends on the choice of the orbitals, variational calculation steps of the two-particle density matrix are interspersed with orbital-optimization steps (based on Jacobi rotations in the space of the spatial orbitals). We also point to the importance of symmetry breaking of the orbitals when performing calculations in a doubly occupied framework.application/pdfhttps://biblio.ugent.be/publication/6953981http://hdl.handle.net/1854/LU-6953981http://dx.doi.org/10.1021/acs.jctc.5b00378https://biblio.ugent.be/publication/6953981/file/6954031engI have transferred the copyright for this publication to the publisherinfo:eu-repo/semantics/restrictedAccessJOURNAL OF CHEMICAL THEORY AND COMPUTATIONISSN: 1549-9618Physics and AstronomyRENORMALIZATION-GROUPANTISYMMETRIC PRODUCTSSPACE SCF METHODCOUPLED-CLUSTER THEORYINITIO QUANTUM-CHEMISTRYNONORTHOGONAL GEMINALSHARTREE-FOCKMOLECULESSTATESALGORITHMVariational optimization of the second-order density matrix corresponding to a seniority-zero configuration interaction wave functionjournalArticleinfo:eu-repo/semantics/articleinfo:eu-repo/semantics/publishedVersion