Abstract
The fully relativistic density-functional theory (RDFT) is employed to calculate interconfigurational energies (ICE's), including s-d transition energies, s- and d-ionization energies for the second and the third transition-metal atoms. Relativistic results from local-spin-density approximation (RLSD), the generalized gradient approximation (RGGA), and the approximation within the framework of the Krieger-Li-Iafrate treatment of the optimized effective potential (ROEP) incorporated by an explicit self-interaction correction term are reported. In addition, results from the simple perturbation procedure are also calculated for comparisons. Among these three exchange-correlation functionals, it is found that the RGGA yields the most accurate ICE's for both the 5s-4d and 6s-5d transition and 4d ionization. For the 5s and the 6s ionization, the ROEP, which is expected to give a good description of the ICE's due to its correct long-range behavior, does not surpass the RLSD and RGGA. It is surprising to find that the simple perturbation method yields the same ICE's with those of the fully RDFT for the second transition -metal atoms. The validity of the perturbative procedure still persists for the lanthanum atom (Z= 57) and then fails dramatically for the rest of the third transition metals, with the f electrons being fully filled. From the similarity of calculations by means of the fully RDFT and the standard perturbation method, we are optimistic that the simple perturbation method not only greatly speeds up the computations in practice, but yields the reliable ICE's, up to La.