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Manuscript Title: Anisotropic and anharmonic effects through the t-matrix for Low- Energy Electron Diffraction (TMAT V1.1).
Authors: P.L. de Andres, D.A. King
Program title: TMAT
Catalogue identifier: ADOT_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 138(2001)281
Programming language: Fortran.
Computer: Alpha ev6-21264(700Mhz).
Operating system: Digital UNIX V5.0.
RAM: 32M words
Word size: 64
Keywords: Solid state physics, LEED, Low-Energy Electron Diffraction, Anisotropic/anharmonic vibrations, Full dynamical theories, Multiple scattering calculations, T-matrix (expansions in cumulants or multipoles).
Classification: 7.2.

Nature of problem:
We describe the FORTRAN-90 program TMAT v1.1 for the computation of non-diagonal t-matrices representing anisotropic and/or anharmonic atomic vibrations. TMAT can be integrated easily in any standard Low-Energy Electron Diffraction program.

Solution method:
The vibration of atoms in an anisotropic and/or anharmonic potential is described by a probability distribution function. By expanding this probability distribution function either in cumulants or in multipoles we compute a scattering t-matrix that represents the effects of thermal vibrations, static disorder and/or anharmonicity in the scattering of electrons by atoms.

Running time:
Using the cumulants method, a single energy takes 2.5 seconds for lmax = 9. Running time scales with lmax^6.

References:
[1] J.B. Pendry, Low-Energy Electron Diffraction, (Academic, 1974).
[2] V. Fritzsche, Phys. Rev. B 50, 1922 (1994).
[3] W. Moritz, J. Landskron, Surf. Sci. 337, 278 (1995).