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Abstract
Our ability to understand and simulate the reactions catalyzed by iron depends strongly on our ability to predict the relative energetics of spin states. In this work, we studied the electronic structures of Fe^{2+} ion, gaseous FeO and 14 iron complexes using KohnSham density functional theory with particular focus on determining the ground spin state of these species as well as the magnitudes of relevant spinstate energy splittings. The 14 iron complexes investigated in this work have hexacoordinate geometries of which seven are Fe(II), five are Fe(III) and two are Fe(IV) complexes. These are calculated using 20 exchangecorrelation functionals. In particular, we use a local spin density approximation (LSDA)  GVWN5, four generalized gradient approximations (GGAs)  BLYP, PBE, OPBE and OLYP, two nonseparable gradient approximations (NGAs)  GAM and N12, two metaGGAs  M06L and M11L, a metaNGA  MN15L, five hybrid GGAs  B3LYP, B3LYP∗, PBE0, B973 and SOGGA11X, four hybrid metaGGAs  M06, PW6B95, MPW1B95 and M08SO and a hybrid metaNGA  MN15. The density functional results are compared to reference data, which include experimental results as well as the results of diffusion Monte Carlo (DMC) calculations and ligand field theory estimates from the literature. For the Fe^{2+} ion, all functionals except M11L correctly predict the ground spin state to be quintet. However, quantitatively, most of the functionals are not close to the experimentally determined spinstate splitting energies. For FeO all functionals predict quintet to be the ground spin state. For the 14 iron complexes, the hybrid functionals B3LYP, MPW1B95 and MN15 correctly predict the ground spin state of 13 out of 14 complexes and PW6B95 gets all the 14 complexes right. The local functionals, OPBE, OLYP and M06L, predict the correct ground spin state for 12 out of 14 complexes. Two of the tested functionals are not recommended to be used for this type of study, in particular M08SO and M11L, because M08SO systematically overstabilizes the high spin state, and M11L systematically overstabilizes the low spin state.
Original language  English (US) 

Pages (fromto)  1304913069 
Number of pages  21 
Journal  Physical Chemistry Chemical Physics 
Volume  19 
Issue number  20 
DOIs  
State  Published  2017 
Bibliographical note
Publisher Copyright:© the Owner Societies 2017.
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 1 Finished

NMGC: Nanoporous Materials Genome: Methods and Software to Optimize Gas Storage, Separations, and Catalysis (Phase 1)
Siepmann, I. (PI), Cramer, C. (CoI), Gagliardi, L. (CoI), Truhlar, D. G. (CoI), Tsapatsis, M. (CoI) & Goodpaster, J. D. (CoI)
9/1/12 → 8/31/17
Project: Research project