THE THOMAS-FERMI TYPE SCREENING OF THE CRYSTAL-FIELD MULTIPOLE MOMENTS

Using a nonintegral expansion method of screened potentials about a di splaced center (by a) the intrinsic crystal-field terms generated by t he point charge, dipole, and quadrupole moments of a ligand have been quantitatively estimated, The calculation has been performed within th e Thomas-Fermi model for the screening radius 1/lambda greater than or equal to a/3. In contrast to an almost total attenuation of the monop ole component (of no contribution to the crystal-field splitting) the screening efficiency for higher crystal-field terms regularly drops. T he screening factor for the fourth-order terms does not exceed 0.5 and that for the sixth-order, 0.3. In the case of the second-order crysta l-field terms a particular situation is observed. Their screening fact or for the point-charge potential reaches 0.6 for lambda a = 3 but con tributions generated by the dipole and quadrupole components are sever al times enhanced. This fact may explain some interpretation difficult ies occurring often in the case of the second-order parameters and con cerning both their magnitude and sign. (C) 1996 Academic Press, Inc.