Semiclassical model of ions: subshell ionization energies

A simple semiclassical model for fast estimations of outer-and inner-subshell ionization energies of atoms and ions is presented. The energies are calculated from the quantization condition with analytical potential. The quantum defect approximation for Rydberg states is developed and the relativistic correction is derived. Comparisons with experimental data and more accurate numerical calculations are made. The accuracy of the model is found to be comparable with that of the Hartree-Fock-Slater approximation. (author)