Electronic structure and optical transition energies of theUcenter in alkaline-earth fluorides

The self-consistent-field multiple-scattering method in the $X\ensuremath{\alpha}$ approximation is used to calculate the electronic structure and the optical transition energies of the $U$ center in Ca${\mathrm{F}}_{2}$, Sr${\mathrm{F}}_{2}$, and Ba${\mathrm{F}}_{2}$.