NON-MUFFIN-TIN ATOMIC SCATTERING-MATRICES FOR SEMICONDUCTOR LEED-CALCULATIONS

Non-muffin-tin Potentials for LEED-calculations can be treated by the integration of the Lippmann-Schwinger equation as described by Nagano and Tong. We have solved this coupled system of equations numerically with a code for ordinary differential equations. The general scattering potential is generated by superimposing atomic Clementi-Roetti densities and Coulomb potentials for a cluster of crystal atoms. The exchange potential is modeled as a function of the superimposed electron density. Both, energy-dependent and energy-independent exchange potentials are investigated. The spherical wave decomposition of the potential entering the angular momentum representation of the Lippmann-Schwinger equation is performed with an efficient numerical integration algorithm. Spherical wave components of the superposition potential are shown to emphasize their influence on the LEED-calculation. Scattering amplitudes of this potential model are computed and compared with those of standard muffin-tin phase shifts of GaAs. Especially, surface configurations are considered within this procedure.