On the accuracy of gradient corrected density functional methods for transition metal complexes

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Abstract
Density functional theory with gradient corrections (DFTG) is applied to a series of second‐row transition metal compounds. The mean absolute deviations from experiment for the atomic excitation energies and ionization potential are in the range 0.2–0.4 eV. In comparison with accurate multireference configuration interaction (MR‐CI) and parametrized CI with parameter 80 (PCI‐80) results for the binding energies of the MCH+ 2 cations, the mean absolute deviation is 6.7 kcal/mol to be compared with 17.8 kcal/mol at the modified coupled pair functional (MCPF) level. The DFTG result is more sensitive to the choice of asymptote with a mean deviation of 14 kcal/mol if the bonding atomic state is not used as asymptote. Product energies and transition states for the addition of methane to RhXL (X=H, Cl, L=H2O, NH3, PH3, and CO) also show the same trends as the PCI‐80 comparison and represent an improvement over the MCPF results.