Calculation of the electronic structure of color centers by the multiple-scattering method

The electronic structure of the $U$, $F$, $U_1$, and $U_2$ centers in KCl has been studied using the self-consistent multiple scattering (or scattered wave) $X\alpha$ method. In these calculations, clusters including the first-nearest neighbors are used to find the peak energies of various absorption bands. The calculated energies for the $U$ and $F$ centers agree well with the experiment. In the case of the $U_2$ center, two possible transitions are investigated and one agrees well with the experimental value while the other, a charge-transfer process, gives an energy too small. The hyperfine interaction of the $U_2$ center and the optical absorption of the $U_1$ center have also been studied.