Assessment of DFT functionals for a minimal nitrogenase [Fe(SH)4H]- model employing state-of-the-art ab initio methods

Victor P Vysotskiy; Magne Torbjörnsson; Hao Jiang; Ernst D Larsson; Lili Cao; Ulf Ryde; Huanchen Zhai; Seunghoon Lee; Garnet Kin-Lic Chan

doi:10.1063/5.0152611

Assessment of DFT functionals for a minimal nitrogenase [Fe(SH)4H]- model employing state-of-the-art ab initio methods

J Chem Phys. 2023 Jul 28;159(4):044106. doi: 10.1063/5.0152611.

Authors

Victor P Vysotskiy¹, Magne Torbjörnsson¹, Hao Jiang¹, Ernst D Larsson¹, Lili Cao¹, Ulf Ryde¹, Huanchen Zhai², Seunghoon Lee², Garnet Kin-Lic Chan²

Affiliations

¹ Department of Computational Chemistry, Lund University, Chemical Centre, SE-221 00 Lund, Sweden.
² Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.

PMID: 37486046
DOI: 10.1063/5.0152611

Abstract

We have designed a [Fe(SH)4H]- model with the fifth proton binding either to Fe or S. We show that the energy difference between these two isomers (∆E) is hard to estimate with quantum-mechanical (QM) methods. For example, different density functional theory (DFT) methods give ∆E estimates that vary by almost 140 kJ/mol, mainly depending on the amount of exact Hartree-Fock included (0%-54%). The model is so small that it can be treated by many high-level QM methods, including coupled-cluster (CC) and multiconfigurational perturbation theory approaches. With extrapolated CC series (up to fully connected coupled-cluster calculations with singles, doubles, and triples) and semistochastic heat-bath configuration interaction methods, we obtain results that seem to be converged to full configuration interaction results within 5 kJ/mol. Our best result for ∆E is 101 kJ/mol. With this reference, we show that M06 and B3LYP-D3 give the best results among 35 DFT methods tested for this system. Brueckner doubles coupled cluster with perturbaitve triples seems to be the most accurate coupled-cluster approach with approximate triples. CCSD(T) with Kohn-Sham orbitals gives results within 4-11 kJ/mol of the extrapolated CC results, depending on the DFT method. Single-reference CC calculations seem to be reasonably accurate (giving an error of ∼5 kJ/mol compared to multireference methods), even if the D1 diagnostic is quite high (0.25) for one of the two isomers.