On the use of parameters in crystal field theory and related calculations

General criteria for the use of empirical parameters as an alternative to detailed first principle calculations of complex many electron problems are discussed. It is suggested that whenever “useful theoretical accuracy” cannot be obtained, the experimental data are more meaningfully analyzed in terms of empirically fitted parameters, using the theory only for establishing the correct form of the Hamiltonian and predicting which parameters may safely be neglected. The application of these criteria is illustrated for the case of crystal field theory.