The superposition model of crystal fields

TLDR

The superposition model was devised to disentangle geometrical and physical contributions to crystal field parameters and has proven effective for lanthanide spectra, with a parallel success of the angular overlap model for d‑electron spectra. This paper reviews the core concepts, application methodology, and reliability of the superposition model while clarifying its relationship to the angular overlap model. The authors detail recent developments, including applying the model to ground‑state multiplet splittings of d⁵ and f⁷ ions, orbit‑lattice interactions, transition intensities, correlation crystal fields, and critically assess evidence supporting or refuting the model’s postulates.

Abstract

The superposition model was originally developed to separate the geometrical and physical information in crystal field parameters. Its success in the analysis of lanthanide spectra has been paralleled by the success of the related angular overlap model in the analysis of d-electron spectra. The basic ideas, method of application and reliability of the superposition model are discussed and its relationship with the angular overlap model is clarified. Developments described are the application of the superposition model to the ground (L=0) multiplet splittings of d5 and f7 ions, orbit-lattice interactions, transition intensities and correlation crystal fields. Special attention is paid to work which has been claimed to support or disprove the postulates of the model.