DFT Calculations Of Crystal-field Parameters Of The Lanthanide Ions In The LaCl₃Crystal

Crystal-feld （CF） models have been commonly used to characterizethe interactions of lanthanide （Ln） ions with their environments incrystalline hosts. In these models, the number of CF parameters isdetermined by the site symmetry of the Ln ion, and the parameter valuesare obtained by ftting to the experimental energy level structure deducedfrom high-resolution absorption and emission spectra. When thecomplexity of the local environment is increased or the site symmetry islow, the number of CF parameters will probably exceed the number ofobservables.We present herein a calculation of crystal-feld （CF） parameters forthe lanthanide ions in the LaCl₃crystal, using the density functionaltheory-based orbital-free embedding formalism in conjunction with theeffective Hamiltonian method. The calculated values for the second-andfourth-rank CF parameters agree fairly well with the experimental data. Itis found that the effect of ligand polarization plays a crucial role indetermining the sign and magnitude of the second-rank CF parameters,while the effect of Pauli repulsion between4f electrons and the ligands isimportant for the fourth-rank CF parameters. The usefulness of thepresent approach is illustrated by a study of the relative preference ofEu³⁺occupation on the two distinct Pb²⁺sites in the KPb₂Cl₅crystal. Thecomputational approach and results discussed in this work are useful for a better understanding and simulation of the CF effect in thelanthanide-containing systems.