Determine the more accurate correlated treatment for dysprosium crystal-field parameters

Determine whether CASPT2 or NEVPT2 provides more accurate crystal-field parameters for the model dysprosium(III) complex [Dy(C5H5)2]+ when the two calculations use different computational workflows and basis sets.

Background

The paper compares crystal-field parameters obtained for [Dy(C5H5)2]+ using OpenMolcas/CASPT2 and ORCA/NEVPT2. Although the two approaches produce broadly similar results, they differ substantially for some parameters, particularly B40: CASPT2 increases this parameter whereas NEVPT2 decreases it. The comparison is further complicated because the calculations employ different basis sets and computational protocols.

Because no established reference value is available for the model complex, the paper leaves unresolved which correlated treatment yields the more accurate crystal-field description. Resolving this issue would require controlled methodological tests using comparable computational settings or an independent benchmark.

References

In the absence of a well-established reference, it is difficult to assess which of the two results is more accurate.

— The NewMag crystal-field code for f-element systems: Implementation for extended active spaces, second-order correlated energies, and generalisation to fn configurations  (2609.37541 - Duplaix-Rata et al., 29 Sep 2026) in Section 4.3.1, “Application to a model dysprosium(III) complex (f9)”