Ab initio studies of electron correlation in rare-earth ions. II. Non-transferable intershell correlation effects for 4f2in Pr3+

The effect of non-transferable intershell correlation effects on the energies of the LS states determined by the 4f 2 electronic shell is studied for Pr 3+ by means of a series of configuration interaction calculations defined in terms of configuration state functions (CSF). Some attention is paid to the problem of dealing with the large number of CSF corresponding to a single orbital configuration but characterised by various coupling schemes of the spin and orbital angular momenta. It turned out that the dominant internal, semi-internal and core polarisation effects are represented by configurations corresponding to the excitations 4d 2 to 4f 2 , 4d 2 to 4f5f, and 5s to 5d, respectively. The latter configuration has the strongest effect on the LS term energy differences.