Performance
of Density Functionals for Activation Energies of Zr-Mediated Reactions
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Abstract
Coupled cluster CCSD(T) calculations
with core–valence correlation and complete basis set (CBS)
limit extrapolation are used to benchmark the performance of commonly
used density functionals in computing energy barriers for Zr-mediated
reactions involving zirconocene species. These reactions include (a)
insertions of the Zr–H bond of Cp<sub>2</sub>Zr(H)Cl into CC,
CC, and CO bonds and (b) C–H activations by
ZrN bond in Cp<sub>2</sub>ZrNH. The best performing
functionals are M06-L, M06, and M06-2X in the M06 series, all having
mean unsigned deviations (MUD) less than 2 kcal/mol. The worst performing
functional is OLYP, with a distinctly large MUD of more than 10 kcal/mol.
Considering also the trends in barrier heights and the systematic
barrier height deviation, our best recommended functional is M06-2X.
In this work, DFT empirical dispersion correction (DFT-D3) is found
to improve the performance of barrier height values for most functionals
(especially of OLYP and B3LYP). With DFT empirical dispersion correction,
we also recommend M06-2X for reaction barrier calculations of Zr-mediated
reactions