Geometries of Transition-Metal Complexes from Density-Functional Theory.

Several levels of density functional theory, i.e., various combinations of exchange-correlation functionals and basis sets, have been employed to compute equilibrium geometries for a diverse set of 32 metal complexes from the first transition row, for which precise gas-phase geometries are known from electron diffraction or microwave spectroscopy. Most DFT levels beyond the local density approximation can reproduce the 50 metal-ligand bond distances selected in this set with reasonable accuracy, as assessed by mean and standard deviations of optimized vs observed values. The ranking of some popular functionals, ordered according to decreasing standard deviation, is BLYP ≈ HCTH > B3LYP > BP86 > TPSS ≈ TPSSh. Together with its hybrid variant, the recently introduced meta-GGA functional TPSS performs best of all tested functionals, with mean and standard deviations of -0.5 and 1.4 pm, respectively. Even smaller errors are found for a more compact but less diverse set of transition-metal mono- and dihalides, for which experimentally derived equilibrium geometries are available.