Effect of the ligand charge distribution on the crystalline electric field of rare-earth ions

The effect of the overlap between the magnetic electron wave function of the central Pr 3+ ion and the electronic wave function of the nearest Cl - ions on the crystal-field parameters of the Pr 3+ ion in a PrCl 3 crystal has been estimated. The Coulomb part of the overlap contribution, which always opposes the point-charge contribution, to A 6 0 < r 6 > and A 6 6 < r 6 > is nearly double the point-charge contribution, while for A 4 0 < r 4 > and A 2 0 < r 2 > it is 89% and 23%, respectively, of the point-charge contributions. The effect of the overlap correction to the parameters calculated by Hutchings and Ray on the basis of the point-electric-moment model of the ligands has been estimated. The calculation emphasizes the need for a detailed molecular-orbital treatment of crystal-field splitting of the energy levels of rare-earth ions, possibly allowing for the covalency.