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Manuscript Title: LEED intensity curves by the layer-by-layer method and perturbation calculation.
Authors: J. Rundgren, A. Salwen
Program title: LEED BY LAYERS AND PERTURBATION
Catalogue identifier: ACKE_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 7(1974)369
Programming language: Fortran.
Computer: IBM 360/75.
Operating system: GUTS.
RAM: 98K words
Word size: 32
Keywords: Solid state physics, Low energy, Electron diffraction, Leed, Surface structure, Adsorbed layers, Electron scattering, Layer-by-layer method, Perturbation Calculation, Structure constants, Lattice sums, Muffin-tin.
Classification: 7.2.

Other versions:
Cat Id Title Reference
ACKG_v1_0 LEED BEAM-SYMMETRIZED CPC 9(1975)312

Revision history:
Type Tit le Reference
correction 000A CORRECTION 28/02/75 See below

Nature of problem:
Experiments with low energy electron diffraction (LEED) are used for investigating the structure of the surface regions of pure crystals and of crystals covered with an adsorbate. The diffraction pattern is observed and the intensities of the diffracted beams are recorded as functions of energy and direction of the incident electrons. In order to find the composition of the unit mesh of the surface structure, a model is proposed for the lattice of the substrate plus overlayer, and LEED intensity curves are calculated. A LEED intensity program is presented in this work.

Solution method:
It is supposed that the surface structure can be sliced into well separated atomic layers, the two-dimensional lattices of which contain one atom per unit cell. The multiple scattering of the electrons by the sliced structure is calculated by means of the layer-by-layer method. The periodic Green's function of a layer is calculated using direct lattice summation. The fluxes of the beams reflected by a series of layers are calculated with the aid of the perturbation method for renormalized forward scattering. The program is based on the muffin-tin approxiamtion to the periodic potential of the surface region. The phase shifts representing the scattering of the low energy electrons by the muffin-tins are required as input to the program.

Restrictions:
The program can take at most 5 phase shifts and 21 beams.

Running time:
The intensity of a diffraction pattern corresponding to a single energy and direction of incidence takes 3.4 s, when the number of beams is fixed at 21 and the accuracy of beam intensity is 0.001. If the number of beams is adjusted by the program against the energy, intensity versus energy-curves are calculated more economically. Under these circumstances patterns calculated at equal intervals between 20 and 100 eV take on the average 1.7 s/pattern.

CORRECTION SUMMARY
Manuscript Title: Unpublished correction to LEED intensity curves by the layer-by-layer method and perturbation calculation.
Authors: J. Rundgren, A. Salwen
Program title: 000A CORRECTION 28/02/75
Catalogue identifier: ACKE_v1_0
Distribution format: gz
Classification: 7.2.