Inadequacy of the Fitted Crystal‐Field Parameterizations. Case Study: The Fourth‐Order Crystal‐Field Splitting Moment in Cubic Systems.

To facilitate the calculation of the fourth‐order crystal‐field (CF) splitting moment, which in a complex way depends on the split state |J⟩, a time saving formula is elaborated, which is positively verified for several cubic systems RE3+: Cs2NaLaCl6. The appropriate crystal‐field parameters (CFPs) have to be substituted to the presented formula. However, the question is which ones. The clear answer proven in the paper is that single‐state CFPs should necessarily be used. To test the approach, a few cubic systems, for which such single‐state CFPs are available, have been studied. Conventionally fitted CFPs, averaged over the entire electron configuration, do not satisfy the equation, which contradicts the fundamental principle of the CF theory. Such verification significantly limits the physical meaning and applicability of the conventional HCF fitted parameterizations. [ABSTRACT FROM AUTHOR]