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Manuscript Title: Computation of photo-electron and Auger-electron diffraction II: multiple scattering cluster calculation, PAD2.
Authors: G.R. Harp, Y. Ueda, X. Chen, D.K. Saldin
Program title: PAD2
Catalogue identifier: ADIA_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 112(1998)80
Programming language: Fortran.
Computer: DEC-Alpha workstation.
Operating system: UNIX.
RAM: 8.8M words
Word size: 64
Keywords: Angle resolved, Core level, Photoelectron, Auger, Electron diffraction, Surface structure, Multiple scattering, Electron spectroscopy, Solid state physics.
Classification: 7.2.

Subprograms used:
Cat Id Title Reference
ADHZ_v1_0 PAD1 CPC 112(1998)67

Nature of problem:
The program PAD2 evaluates the transmission matrix relating the wavefunction of an electron immediately after its emission from an atom to its wavefunction outside a sample, where it may be detected. This matrix is expressed in an angular-momentum basis centered on the emitting atom.

Solution method:
The electron transmission matrix is evaluated by means of an algorithm which first calculates the scattering matrices of a series of concentric shells centered on the emitter. The scattering between the shells is computed by matrix operations on the shell scattering matrices. Both the intra- and inter-shell scattering may be evaluated by taking account of all multiple scattering processes, or by a choice of approximation schemes of increasing accuracy (and of required computer resources).

Restrictions:
For photoelectron diffraction, the present codes are restricted to just s, p, d, and f core electrons.

Unusual features:
For correct results, this program should be compiled using the DOUBLE PRECISION option of the compiler.

Running time:
The running time of this program is very dependent on the degree of symmetry of the cluster of atoms centered on the emitter. It is also determined by the size of this cluster and the number of spherical-wave components required to represent the various wave fields computed by the program. For the test data provided, PAD2 took 1 minute and 49 seconds on a Silicon Graphics Indigo computer with an R10000 processor. For other data sets it could take considerably longer.

References:
[1] D.K. Saldin, G.R. Harp, and X. Chen, Phys. Rev. B 48 (1993) 8234.