Theory ofFA-center optical absorption in alkali halides: Lattice statics analysis

$F_A$-center optical absorption is analyzed theoretically for 12 doped alkali halides, including two with heavy impurities. The ground state is estimated variationally, including static-lattice distortion. A form of the ion-size correction of Bartram, Stoneham, and Gash is found to give good qualitative, and some quantitative, agreement with experimental values of absorption energies and splittings. Details are given of lattice distortion in the ground state and of the contributions from kinetic, point-ion, and ion-size energies to the absorption splitting.