The spin-state orderings in nine Fe(II) and Fe(III) complexes with ligands of diverse ligand-field strength were investigated with multiconfiguration pair-density functional theory (MC-PDFT). The performance of this method was compared to that of complete active space second-order perturbation theory (CASPT2) and Kohn-Sham density functional theory. We also investigated the dependence of CASPT2 and MC-PDFT results on the size of the active-space. MC-PDFT reproduces the CASPT2 spin-state ordering, the dependence on the ligand field strength, and the dependence on active space at a computational cost that is significantly reduced as compared to CASPT2.
Bibliographical noteFunding Information:
This work was supported in part (L.G. and D.G.T.) by the AFOSR Grant FA9550-16-1-0134. I.C. received funding from the European Research Council (ERC) under the European Union?s Horizon 2020 research and innovation program (Grant Agreement No. 648558, STRIGES CoG grant).
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