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Manuscript Title: ABSFAC: a program for the calculation of the absorption during scattering in multifaceted crystals and similar samples.
Authors: R.C. Clark, J.S. Reid
Program title: ABSFAC
Catalogue identifier: ADHT_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 111(1998)243
Programming language: Fortran.
Computer: Sun Sparc 10.
Operating system: Unix.
RAM: 2K words
Word size: 64
Keywords: Crystallography, Absorption, X-ray scattering.
Classification: 8.

Nature of problem:
The calculation of the absorption during scattering of X-rays in crystals; the scattering of neutrons and other radiation from polyhedral samples satisfying the basic assumptions.

Solution method:
The calculation is done exactly by dividing the sample into Howells polyhedra and using a formula that allows the contribution from each edge of the polyhedra to be cumulated as they are found.

Restrictions:
These are determinded by the memory available. A parameter statement allows the size of arrays to be easily changed if required. The program has been used successfully on samples with 120 faces.

Unusual features:
  1. The program can be used to calculate the absorption in samples that are only partly illuminated by the X-ray beam.
  2. An estimate of the numerical error in the output is provided by the program.

Running time:
For samples with less than 10 faces, about 15ms for each sample orientation or different value of the scattering vector. For a sample with 74 faces, about 3 to 5 seconds per point.

References:
[1] R.C. Clark and J.S. Reid, Acta. Cryst. A51(1995)887.