Tensor LEED for the approximation of nondashspherical atomic scattering

Abstract

We present a new approach to consider nondashspherical atomic charge densities for the computation of intensities in low energy electron diffraction (LEED). This might be important for covalently bonded atoms for example in adsorbed molecules, semiconductors or compound materials. In a first step the nondashspherical charge distribution of a surface atom is approximated by Hartree-Fock calculations applied to a small atomic cluster surrounding the atom under consideration. Then, starting with 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 nondashdiagonal. Eventually, this is made to enter the perturbation scheme tensor LEED. This procedure allows easy access to trial structures with realistic atomic scattering. We applied the method to an example of practical importance, i.e. to the unreconstructed Si(100) surface. A rough estimation neglecting multiple scattering between the nondashspherical and spherical part of the atomic potential proves, however, that the influence of nondashspherical scattering on intensities in a typical energy range (20–150 eV) is practically negligible.