MCSCF study of the avoided curve crossing of the two lowest 1Σ+ states of LiF

Potential energy, dipole moment, and transition moment functions have been calculated for the two lowest 1Σ+ states of LiF using MCSCF wave functions. By optimizing both states simultaneously with a particular choice of configurations it is possible to account for the major part of the correlation energy difference of the neutral and ionic states and to obtain the correct separation of the states at infinite internuclear distance. A simple method to obtain a diabatic description of the two states is proposed. In the crossing region nonadiabatic coupling elements have been calculated.