Impurity States in Ionic Crystals: a Self-Interaction - Corrected Local Spin Density Theory Study.

While the local spin density theory (LSD) has been successfully used to calculate the electronic properties of a variety of condensed matter systems, its use does not provide an adequate description of point impurities in insulating crystals. Unphysical self-interaction effects in LSD lead to calculated one-electron properties which do not agree well with corresponding experimental properties in the limit of localized states. As an additional result of the spurious self-interactions, LSD calculations underestimate the host crystal band gaps in these systems by typically 40%. Recently the self-interaction-correction (SIC) was developed to remove the non-physical effects of electronic self-interaction from LSD. The resulting SIC-LSD theory is self-interaction free, and its use greatly improves the description of both localized states and insulator band gaps compared to uncorrected LSD. In the first part of this work, a novel method for calculating multiplet -dependent atomic wave functions in SIC-LSD is described, and calculated SIC-LSD wave functions for the quintet and triplet excited states of atomic oxygen are shown to be in excellent agreement with the corresponding Hartree-Fock wave functions, further establishing the success of SIC -LSD in calculating the properties of localized states. SIC -LSD is then applied to the NaCl:Cu^+ and LiCl:Ag^+ impurity systems. Transitions associated with the impurity ions in these systems are studied, and the calculated transition energies are found to be in good agreement with experiment. By examining the impurity state wave functions, characteristic differences between the absorption spectra for the Cu^+ and Ag^+ systems are explained.