Simple model for Crystal Field Theory
  We investigate a simple model for the prediction of the splitting of the $3d$ orbitals of a metal ion in the environment of ligands. The electrons are considered to be independent and their interaction with the ligands is represented by the Dirac delta function in three dimensions. We discuss several cases where the model is successful and a few ones where it is not. 
Francisco M. Fern\'andez
cond-mat.mtrl-sci quant-ph