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Manuscript Title: Fourier analysis of EXAFS data, a self-contained Fortran program package.
Authors: E. Indrea, N. Aldea
Program title: EXAFS 1,2,3,4,5
Catalogue identifier: ACUF_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 21(1980)91
Programming language: Fortran.
Computer: FELIX C-256.
Operating system: SIRIS 2/3.
RAM: 54K words
Word size: 32
Peripherals: disc.
Keywords: Surface, X-ray, Absorption, Solid state physics, Local structure, Spectroscopy.
Classification: 7.2.

Nature of problem:
The extended X-ray absorption fine structure (EXAFS), consists of the modulation of the absorption X-ray coefficient in the vicinity of the absorption edge that characterizes the elements in the material. Such modulation, called fine structure, is present because photoelectrons released from the X-ray absorbing atoms backscatter coherently from the neighbouring atoms. Structural information obtainable by Fourier transform of the EXAFS function consists of bond distances, a measure of disorder in bond distances due both to thermal and structural disorder, coordination number and chemical identity of the coordination shell. The present program package performs the calculation of the normalized EXAFS data, the associated Fourier transform and the best- fit value of the structural parameters fot the first coordination shell.

Solution method:
The smoothing and the interpolation of the incident and transmitted X-ray intensity-energy function, is done by 3rd order polynomial functions and by Newton's interpolation formula for unequally spaced values of the argument. The Fourier transform of the EXAFS function was performed by Filon's quadrature formulae. The best fit values of structural parameters were computed by means of an iterative non-linear- parameters least-squares procedure.

Restrictions:
The maximum number of the absorption coefficient values in the present version is 500.

Running time:
The time for the complete test case is 2 min.