ROLE OF THE ELECTROSTATIC MODEL IN CALCULATING RARE-EARTH CRYSTAL-FIELD PARAMETERS

The Sternheimer method is used to derive shielding parameters and anti shielding factors for the whale series of rare earths using relativist ic wavefunctions. It is found that the shielding parameter sigma(2) of the 4f electronic shell is decreased compared to earlier calculations . The sigma(4) and sigma(6) parameters are calculated for the first ti me for all rare-earth ions. In all cases, they are found to be small. The influence of the various calculated parameters on the crystal-fiel d parameters for the cases Nd:LiYF4 and Pr:LiYF4 is studied. Present c orrections result in ab initio crystal-field parameters that are in ex cellent agreement with experimentally fitted phenomenological paramete rs. The nuclear antishielding factors gamma(infinity) are found to ess entially agree with earlier findings. These are also found to agree wi th some early experiments. The various wavefunctions used are derived from a relativistic Desclaux code. These are mon external compared to standard Hartree-Fock wavefunctions. (C) 1998 Elsevier Science S.A.