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Manuscript Title: Molecular t-matrices for Low-Energy Electron Diffraction (TMOL v1.1)
Authors: Maria Blanco-Rey, Pedro de Andres, Georg Held, David A. King
Program title: TMOL
Catalogue identifier: ADUF
Journal reference: Comput. Phys. Commun. 161(2004)166
Programming language: FORTRAN-90/95 (Compaq True64 compiler, and Intel Fortran Compiler 7.0 for Linux).
Computer: Alpha ev6-21264 (700Mhz) and Pentium-IV.
Operating system: Digital UNIX V5.0 and Linux (Red Hat 8.0).
RAM: minimum 64 Mbytes, it can grow to more depending on the system considered.
Word size: 64 and 32 bits
Keywords: Low-Energy Electron Diffraction, Multiple-Scattering, Molecular t-matrix, Non-diagonal t-matrix.
Classification: 7.2.

Nature of problem:
We describe the FORTRAN-90 program TMOL (v1.1) for the computation of non-diagonal scattering t-matrices for molecules or any other poly-atomic sub-unit of surface structures. These matrices can be used in an standard Low-Energy Electron Diffraction program, such as LEED90 or CLEED.

Solution method:
A general non-diagonal t-matrix is assumed for the atoms or more general scatterers forming the molecule. The molecular t-matrix is solved adding the possible intramolecular multiple scattering events using Green's propagator formalism. The resulting t-matrix is referred to the mass centre of the molecule and can be easily translated with these propagators and rotated applying Wigner matrices.

Running time:
Calculating the t-matrix for a single energy takes a few seconds. Time depends on the maximum angular momentum quantum number, lmax, and the number of scatterers in the molecule, N. Running time scales as l6max and N3.

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