title: Multireference Perturbation Theory with Cholesky Decomposition for the Density Matrix Renormalization Group.
abstract: We present a second-order N-electron valence state perturbation theory (NEVPT2) based on a density matrix renormalization group (DMRG) reference wave function that exploits a Cholesky decomposition of the two-electron repulsion integrals (CD-DMRG-NEVPT2). With a parameter-free multireference perturbation theory approach at hand, the latter allows us to efficiently describe static and dynamic correlation in large molecular systems. We demonstrate the applicability of CD-DMRG-NEVPT2 for spin-state energetics of spin-crossover complexes involving calculations with more than 1000 atomic basis functions. We first assess, in a study of a heme model, the accuracy of the strongly and partially contracted variant of CD-DMRG-NEVPT2 before embarking on resolving a controversy about the spin ground state of a cobalt tropocoronand complex.
authors.affiliation: ETH Zürich, Laboratorium für Physikalische Chemie, Vladimir-Prelog-Weg 2, 8093 Zürich, Switzerland.
authors.forename: Leon
authors.initials: L
authors.lastname: Freitag
authors.affiliation: ETH Zürich, Laboratorium für Physikalische Chemie, Vladimir-Prelog-Weg 2, 8093 Zürich, Switzerland.
authors.forename: Stefan
authors.identifier: http://orcid.org/0000-0001-9818-2372
authors.initials: S
authors.lastname: Knecht
authors.affiliation: Dipartimento di Scienze Chimiche e Farmaceutiche, Università di Ferrara , Via Fossato di Mortara 17, 44121 Ferrara, Italy.
authors.forename: Celestino
authors.initials: C
authors.lastname: Angeli
authors.affiliation: ETH Zürich, Laboratorium für Physikalische Chemie, Vladimir-Prelog-Weg 2, 8093 Zürich, Switzerland.
authors.forename: Markus
authors.identifier: http://orcid.org/0000-0002-9508-1565
authors.initials: M
authors.lastname: Reiher