A finite fragment of the crystal lattice can be used as a model for the description of some properties of infinite crystal. In the approach presented by Mickhail V. Ryzhkov, Alexei Mirmelstein, Sung-Woo Yu, Brandon W. Chung, and James G. Tobin on page 1957, the crystal fragment is divided into two parts: the “core” (in blue) and the “shell”. The “shell” includes the atoms from 1 to 5 coordination spheres surrounding the “core”. The electron densities and the potential of the atoms in the “shell” are replaced by the corresponding values obtained for the crystallographically equivalent centers of the cluster “core”. This approach can be used successfully for the description of some properties of solid actinide compounds and is able to reproduce the relevant experimental features observed by resonant photoelectron spectroscopy (RESPES).