Ab initio calculation of crystal-field correlation effects in Pr³⁺-Cl^-

Many-body perturbation theory, with non-orthogonal basis states, has been used to determine covalency, overlap and ligand polarisation contributions to the intrinsic crystal-field and correlation crystal-field parameters for the system Pr³⁺-Cl^- spaced as in PrCl₃. Significant crystal-field contributions are shown to arise from ligand polarisation, but there are no significant contributions to either the Slater parameters or the correlation crystal-field parameters from this mechanism. Calculated values of crystal-field parameters are in reasonable agreement with experiment. A new approach to the phenomenological treatment of crystal-field correlation effects is suggested.