Performance of Density Functionals for Activation Energies of Zr-Mediated Reactions

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 Cp₂Zr­(H)Cl into CC, CC, and CO bonds and (b) C–H activations by ZrN bond in Cp₂ZrNH. 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