Comparative Study of Single and Double Hybrid Density Functionals for the Prediction of 3d Transition Metal Thermochemistry.

The performance of 13 density functionals, including hybrid-GGA, hybrid-meta-GGA, and double-hybrid functionals, in combination with the correlation consistent basis sets, has been evaluated for the prediction of gas phase enthalpies of formation for a large set of 3d transition-metal-containing molecules with versatile bonding features. Of the methods studied, the hybrid B97-1 functional and the double hybrid functional mPW2-PLYP exhibit the best overall performance with mean absolute deviations (MAD) from experimental data of 7.2 and 7.3 kcal mol(-1), respectively. For single reference molecules, where dynamic correlation predominates, the results of the hybrid functionals B97-1, B98, and ωB97X and the double hybrid functionals B2-PLYP, B2GP-PLYP, and mPW2-PLYP yield the smallest deviations from the experimental enthalpies of formation. For the prediction of thermodynamic properties of coordination complexes including metal carbonyls, B97-1 and mPW2-PLYP are the most promising functionals of those investigated. When the size of the molecule is considered, B97-1 and B98 outperform mPW2-PLYP for diatomics and triatomics, while mPW2-PLYP yields the lowest MAD for larger molecules.