Abstract. We propose an efficient method by which previously computationally expensive, but moderately important, pair correlation effects can be incorporated into f n excitation energies. Application is to Gd IV. Secondly, we extend two methods of obtaining static and tensor dipole polarizabilities and apply them to the Ni II ground state. The first uses the sum over f -values approach, and the second is variational.
Calculation of Excitation Energies for Lanthanides and ActinidesOur long term computational interest has been to develop (when necessary) and apply the relativistic configuration interaction (RCI) method to predict properties of complicated atoms and ions -specifically, for transition metals, lanthanides and actinides.Triply ionized lanthanide and actinide ions appear as impurities in condensed matter systems where they can serve as centers of lasing activity [1], play a role in MRI medicine as endohedral metallofullerenes (e.g. Gd 3 N-C 80 ) [2], appear as important constituents of high temperature super-conductors, etc. There also has been interest in the free Gd IV ion as a possible means of detecting an electron electric dipole moment [3].Experimentally, only a few of the low lying excitation energies within the f n configuration are generally known [4,5] from measurements made in the condensed phase. Dipole transition energies f n -f n−1 d are generally not known experimentally, as the d levels in the solid are not very well localized [5]. It also may be noted that most prevalent charge state of the lanthanide/actinide ion in the solid is 3 + [5]. Computationally, these excitation energies are also difficult to obtain [6]. The calculations require the use of a relativistic Hamiltonian (Dirac-Breit) and a correlated wavefunction having at least a first order form, i.e. one that includes all the differentially important single and double subshell excitations from a set of reference functions. At present, a reasonable ab initio accuracy goal for excitations within f n would be to position all levels to ∼1000 cm −1 relative to the ground state. Our recent Gd IV [6] achieved 1257 cm −1 , and we improve this to 838 cm −1 here, accompanied by a drop in calculation time of 67%.