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Chemical insights into the electronic structure of Fe(II) porphyrin using FCIQMC, DMRG, and generalized active spaces

preprint
revised on 01.10.2020 and posted on 01.10.2020 by Oskar Weser, Leon Freitag, Kai Guther, Ali Alavi, Giovanni Li Manni
Stochastic-CASSCF and DMRG procedures have been utilized to quantify the role of the electron correlation mechanisms that in a Fe-porphyrin model system are responsible for the differential stabilization of the triplet over the quintet state. Orbital entanglement diagrams and CI-coefficients of the wave function in a localised orbital basis allow for an effective interpretation of the role of charge-transfer configurations. A preliminary version of the Stochastic Generalized Active Space Self-Consistent Field method has been developed and is here introduced to further assess the pi-backdonation stabilizing effect.
By the new method excitations between metal and ligand orbitals can selectively be removed from the complete CI expansion. It is demonstrated that these excitations are key to the differential stabilization of the triplet, effectively leading to a quantitative measure of the correlation enhanced pi-backdonation.

Funding

Austrian Science Grant Project J 3935-N34

Max-Planck-Gesellschaft

History

Email Address of Submitting Author

oskar.weser@gmail.com

Institution

Max Planck Institut für Festkörperforschung

Country

Germany

ORCID For Submitting Author

0000-0001-5503-1195

Declaration of Conflict of Interest

The authors declare no competing financial interest.

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