Crystal field parameters in rare earth compounds: A mixed ‘‘covalo-electrostatic model’’

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Abstract
A limited LCAO model was applied to a series of 12 rare earth or rare earth doped compounds and one actinide compound, namely, LiYF4:Nd3+, KY3F10:Eu3+, YOCl:Eu3+, BaFCl:Sm2+, SrFCl:Sm2+, Nd2O3, Nd2O2S, NdAlO3, LaAlO3:Eu3+, LaCl3:Nd3+, YF3:Gd3+, Y2O3:Eu3+, and CsUF6. The procedure and the approximations are detailed. The overlap integrals are calculated and fitted to analytical functions of the distance for nine rare earth–ligand pairs: Nd3+, Eu3+, Tm3+/O2−, F−, and Cl− utilizing literature radial wave functions. For each species, the ionization energies are assigned mean values. The one‐electron energies given by the diagonalization of the interaction matrix are transformed into sets of Bkq crystal field parameters. The comparison with literature phenomenological values is made in terms of scale and reliability factors. In most cases the results are satisfactory.