Crystal–field parameters from ab initio calculations

We give a method for extracting an effective Hamiltonian from ab initio calculations that requires only the calculated energies for the model space and the part of the calculated eigenvectors that correspond to the model space. This method simplifies the extraction of phenomenological parameters that can be compared with experiment. We demonstrate the method with an ab initio calculation for d states, which is relevant to examining the 4fN−15d configurations of lanthanide and actinide ions.