Relativistic f↔f transitions in crystal fields: II. Beyond the single-configuration approximation

A relativistic model of f↔f transitions introduced previously is completed here by the third-order contributions caused by electron correlation. The approach is based on the transformation of all tensor operators to their relativistic effective form; the final effective operators that act within the 4f shell are derived by means of the so-called partial closure. The tensorial structure of the new effective operators, that are in general two-particle objects, is discussed and their reduced form is analysed in the light of the standard single-particle parametrization scheme of f↔f transition spectra. (author)