Atomic structure calculations of U and Pu

Actinide atoms with many valence electrons, strong valence-core correlations, and substantial relativistic effects are very challenging for atomic calculations. Using starting potentials that partially include screening by valence electrons, we find that accuracy can be improved and the size of configuration space in the framework of the configuration-interaction (CI) approach can be reduced. In fact, the starting potential with one or two valence electrons removed lead to the dominance of principal configurations, so the perturbation theory can be applied to take into account smaller interactions of these configurations with the others. Thus, the configuration interaction perturbation theory (CI-PT) method can be applied to actinide atoms, such as 8-valence electron Pu. First, it can use an optimal starting potential, second, it can treat the CI effects via computationally much more efficient perturbation theory, and third, the basis is relativistic. Additional fine tuning can be added to improve the accuracy for example by adjusting the energies of configurations. The program was modified to make the parameter adjustments automatic. The results of calculations for various atoms and ions, like U I, U II, Pu II will be presented. Relatively high accuracy has been achieved, and further improvements are possible.