Pairwise additive semi ab initio potential for the elastic scattering of He atoms from the LiF(001) crystal surface

The interaction potential for the elastic diffractive scattering of low-energy He atoms from the highly corrugated LiF(001) crystal surface is derived from semi ab initio pair potentials in the framework of the recently developed Tang--Toennies potential model (J. Chem. Phys. 80, 3726 (1984)). In addition to the sum of all He atom-crystal ion two-body potentials the induced dipole potential caused by the electric field of the ion lattice is taken into account, leaving only one free parameter, the C/sub 6/ dispersion constant of the He--F/sup -/ interaction. By simple adjustment of this parameter, it is possible to fit all of the experimental bound states of the atom-surface potential well, to within experimental error. Diffraction probabilities calculated by the close coupling method with this potential are shown to be in good agreement with the available experimental results. Two different empirical potential models based on the Morse potential are also investigated, but do not provide as good a description of the bound states and diffraction intensities.