Performance of Density Functional Theory for Second Row (4d) Transition Metal Thermochemistry

The performances of 22 density functionals, including generalized gradient approximation (GGA), hybrid GGAs, hybrid-meta GGAs, and range-separated and double hybrid functionals, in combination with the correlation consistent basis sets and effective core potentials, have been gauged for the prediction of gas phase enthalpies of formation for the TM-4d set, which contains 30 second row transition metal-containing molecules. The enthalpies of formation determined by the 22 density functionals were compared to those generated via the relativistic pseudopotential correlation consistent Composite Approach (rp-ccCA), which has a goal of reproducing energies akin to those from CCSD(T,FC1)-DK/aug-cc-pCV∞Z-DK calculations. B3LYP/cc-pVTZ-PP optimized geometries were used in this study, though structures determined by other functionals also were examined. Of the functionals employed, the double hybrid functionals, B2GP-PLYP and mPW2-PLYP, yielded the best overall results with mean absolute deviations (MADs) from experimental enthalpies of formation of 4.25 and 5.19 kcal mol(-1), respectively. The GGA functionals BP86 and PBEPBE resulted in deviations from experiment of nearly 100 kcal mol(-1) for molecules such as molybdenum carbonyls. The ωB97X-D functional, which includes the separation of exchange energy into long-range and short-range contributions and includes a dispersion correction, resulted in an MAD of 6.52 kcal mol(-1).