Configuration mixing and crystal-field splitting of Cr2+ in CdS

The effect of interaction of excited configurations 3d³4s, 3d³4p and 3d³4d with the ground 3d⁴ configuration on the crystal field splitting (E- T₂) of the tetrahedral Cr²⁺ ion in CdS has been studied by a rigorous method in which the energy matrix constructed in a basis of states belonging to both the ground and excited configurations has been directly diagonalised. Such a fairly rigorous treatment yield surprising results and interesting conclusions. Even though the calculation is based on an ionic model of the crystal field, it is found that inclusion of excited configurations accounts for the entire crystal field splitting observed experimentally in this particular case of Cr²⁺ in CdS. The configuration mixing in our treatment yields for the crystal field splitting a result few times greater than that found when the calculation is confined within the ground configuration only. Furthermore, the present investigation indicates that the second order perturbation method used in the earlier treatment was quite inadequate in the case of Cr²⁺ in CdS.