Transition metals are central to nearly all of catalysis and they enlarge the palette for materials discovery. Mechanistic predictions and first-principles material design rely heavily on density functional theory (DFT), due to first-principles description of electronic structure along with affordable computational cost. Periodic DFT studies of transition metal compounds have been mainly limited to semi-local exchange-correlation approximations, often leading to errors in prediction of electronic structure and magnetic properties due to self-interaction error (SIE). Most commonly, SIE is approximately corrected within DFT through i) inclusion of exchange from SIE-free Hartree-Fock (HF), dramatically increasing the cost of periodic calculations or ii) augmentation with a Hubbard U term (DFT+U) applied to the transition-metal orbitals, which has no computational cost. In both cases, the computational chemist must choose either the value of U to employ or the percentage of HF exchange. For prototypical, first-row transition metal compounds (e.g. Mn, Fe), we examine the oxidation-state and ligand-environment dependence of DFT+U, hybrid, and meta-GGA exchange tuning on energetic properties and catalytic turnover frequency predictions in particular. Additionally, we identify the ability of these various density functionals to i) reproduce density descriptors obtained from highly-accurate, multi-reference wavefunction theory and ii) reduce energetic curvature with electron count, a key metric of SIE. Finally, we conclude with discussing the possibility of obtaining improved density functionals via matching of density descriptions between accurate references and approximate exchange functionals, rather than the more common focus on energetic errors alone, and we test the effect these modifications could have on small molecule binding critical for predictions of activity in heterogeneous catalysis.

Exploring the impact of density-functional approximation tuning in predictions of bonding, energetics, and magnetic properties of transition metal catalysts

251st National Meeting (2016)

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