TENSOR LEED FOR THE APPROXIMATION OF NONSPHERICAL ATOMIC SCATTERING

We present a new approach to consider non-spherical atomic charge dens ities for the computation of intensities in low energy electron diffra ction (LEED). This might be important for covalently bonded atoms for example in adsorbed molecules, semiconductors or compound materials. I n a first step the non-spherical charge distribution of a surface atom is approximated by Hartree-Fock calculations applied to a small atomi c cluster surrounding the atom under consideration. Then, starting wit h a LEED reference calculation for spherical scatterers as usual, the deviation from the spherical charge distribution is taken into account by means of the corresponding change of the atomic scattering matrix which becomes non-diagonal. Eventually, this is made to enter the pert urbation scheme tenser LEED. This procedure allows easy access to tria l structures with realistic atomic scattering. We applied the method t o an example of practical importance, i.e. to the unreconstructed Si(1 00) surface. A rough estimation neglecting multiple scattering between the non-spherical and spherical part of the atomic potential proves, however, that the influence of non-spherical scattering on intensities in a typical energy range (20-150 eV) is practically negligible.