Comments on the origin of relativistic crystal fields

A re-examination has been made of the form and the role of equivalent operators which are used to represent the effects of intersite electron-electron interactions. The approach takes into account the relativistic character of both the interaction operator and the electronic wavefunctions. The calculations are based on procedures well known in atomic physics but they are applied here in the context of molecular complexes. New terms are found, in the form of the relativistic crystal field, which originate from the Breit-Pauli operator. Sample calculations of the effective operator coefficients for some terms in the relativistic crystal field have been provided. The role of the relativistic crystal fields has been discussed and illustrated with a number of important reduced matrix elements which involve these operators.