Theory of the electronic states and absorption spectrum of the LiCl:Ag+impurity system

The impurity absorption spectra of ${\mathrm{Ag}}^{+}$ and ${\mathrm{Cu}}^{+}$ impurities in alkali halide hosts show characteristically different features, despite the similar nature of the corresponding free ions. We use the self-interaction-corrected local-spin-density (SIC-LSD) theory to calculate the electronic structure of the ground state (4d) and the 5s and 5p excited states of the LiCl:${\mathrm{Ag}}^{+}$ impurity ion. The method of linear combinations of atomic orbitals is used to determine the wave functions and energy levels. By comparing with previous calculations for LiCl:${\mathrm{Cu}}^{+}$, we are able to attribute the differences in the d→s and d→p transitions in the ultraviolet spectra of these systems to the increased bonding between host crystal and impurity orbitals in LiCl:${\mathrm{Ag}}^{+}$, due to the more extensive nature of the ${\mathrm{Ag}}^{+}$ 4d orbitals. A modification of the earlier SIC-LSD impurity-crystal procedure is introduced to treat the strongly mixed impurity states.