Density functional calculations on first-row transition metals

The excitation energies and ionization potentials of the atoms in the first transition series are notoriously difficult to compute accurately. Errors in calculated excitation energies can range from 1 to 4 eV at the Hartree–Fock level, and errors as high as 1.5 eV are encountered for ionization energies. In the current work we present and discuss the results of a systematic study of the first transition series using a spin-restricted Kohn–Sham density-functional method with the gradient-corrected functionals of Becke and Lee, Yang and Parr. Ionization energies are observed to be in good agreement with experiment, with a mean absolute error of approximately 0.15 eV; these results are comparable to the most accurate calculations to date, the quadratic configuration interaction single, double (triple) QCISD(T) calculations of Raghavachari and Trucks. Excitation energies are calculated with a mean error of approximately 0.5 eV, compared with ∼1 eV for the local density approximation and 0.1 eV for QCISD(T). These gradient-corrected functionals appear to offer an attractive compromise between accuracy and computational effort.