Description of ligand field splitting in terms of density functional theory: Calculations of the split levels of the 2F5/2 and 2F7/2 subterms in CeO and CeF under the weak field coupling scheme

A new method of calculating the split levels of the spectroscopic subterms of lanthanide ions under the weak field coupling scheme was formulated based on the density functional theory (DFT) and ligand field theory. To construct the ligand field potential acting on the 4f electrons of a lanthanide compound, the potential of the molecule was obtained by DFT calculations, the 4f-electron contributions to the potential were removed, and the pseudopotentials of the ligands were added to include the Pauli repulsion between the 4f electrons and ligand electrons. The ligand field potential thus obtained includes the effects of the metal-ligand overlap and covalency on ligand-field splitting. This method was tested by calculating the split levels of the 2F5/2 and 2F7/2 subterms associated with the 4f16s1 and 4f16s2 configurations of CeO and CeF, respectively. Our results are in excellent agreement with experiment and indicate that the split levels of lanthanide compounds can be calculated accurately using our method.