Important correlation effects for the Er 3+ 4 f 11 4 S 3/2 → 4 I 15/2 laser transition energy

Most of the important correlation effects transitions within the 4 f n manifold of rare‐earth atomic ions are identified as coming from three sources: 4 f 2 pair correlations, single excitations from the valence shell and shallow core, and pair excitations where both of the electrons go into the incomplete 4 f subshell (exclusion effects). A method (REDUCE) of managing the large basis sets encountered is discussed. Relativistic configuration interaction calculations are done to obtain the energy of the laser transition (in, e.g., GaN) Er 3+ 4 I 15/2 → 4 S 3/2 , to which correlation contributes ∼4000 cm −1 . The residual error of 864 cm −1 may be due to missing second‐order effects and to truncation of the angular basis. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002