Absorption correction with the SHELX97 package

Paul D. Boyle boyle at laue.chem.ncsu.edu
Wed Jun 4 08:42:36 EST 1997

John Bollinger (jobollin at indiana.edu) wrote:
: My understanding of SHELXA, by the way, is that it performs some sort
: of "refined" absorption correction.  I am not certain whether it is
: along the lines of DIFABS or whether it is some other sort of
: parameterized correction, but I should hope that any crystallographer
: would at the very least hesitate before publishing results that were
: obtained via the use of such a correction.

SHELXA is based on Blessing's model of treating anisotropic absorption
through the use of spherical harmonic functions (see Acta Cryst. (1995)
A51, 33-38), whereas DIFABS (see Acta Cryst. (1983) A39, 158-166) uses
a Fourier series to model the absorption.  The comments Sheldrick makes
in the source code of shelxa.f indicates that he feels nothing is wrong
with the Blessing model, but it is the particular misuse of the model
that SHELXA makes which makes it of dubious value.


Paul D. Boyle			    |	boyle at laue.chem.ncsu.edu
Director, X-ray Structural Facility |	phone: (919) 515-7362
Department of Chemistry - Box 8204  |	FAX:   (919) 515-5079
North Carolina State University     | 
Raleigh, NC, 27695-8204

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