Electronic States of theF-C`enter in Lithium Fluoride. I

The electronic states of the F -center in LiF are theoretically investigated taking account of the detailed atomic structure of the crystal. The Hamiltonian of an F -center including polarization effects is presented. The polarizabilities of the ions in the crystal are determined from the static and high-frequency dielectric constants and the reststrahl frequency. Approximate eigenfunctions and energy levels are calculated with the use of variational wave functions comprising linear combinations of the 2 s and 2 p atomic functions on the six lithium ions adjacent to the missing negative-ion site. For both the ground and excited states, the resulting wave functions have larger coeffcients of the 2 p functions than those of the 2 s functions. The first optical excitation energy is obtained to be somewhat smaller than the experimental value; possible sources of this discrepancy are discussed. The g -factor of the F -center is also computed. A more satisfactory theory will be given in the next paper.