A perturbative approach to J mixing in f-electron systems: Application   to actinide dioxides
  We present a perturbative model for crystal-field calculations, which keeps into account the possible mixing of states labelled by different quantum number J. Analytical J-mixing results are obtained for a Hamiltonian of cubic symmetry and used to interpret published experimental data for actinide dioxides. A unified picture for all the considered compounds is proposed by taking into account the scaling properties of the crystal-field potential. 
N. Magnani, P. Santini, G. Amoretti, R. Caciuffo