Modification of X-ray atomic scattering factors in electic fields - validation of the shell model

Quantum-mechanical calculations of the modification of the X-ray scattering factor of an atom/ion in an electric field are compared with predictions of the semi-classical shell model. If the shell parameters are fitted to the dipole polarizability of the ion, the shell model is a very good representation of the scattering factor of the deformed ion, giving support to its use in estimating the effect of ionic deformation on X-ray diffuse scattering and X-ray Debye-Waller factors.