DELABS - DELTA-F Based Correction
ABSORPTION CORRECTION TOOLS
PLATON HOMEPAGE
The DELABS filter in PLATON for empirical absorption correction
requires two inputfiles:
- shelxl.hkl : (SHELX HKLF 4 + Direction Cosines) reflection file
- shelxl.res : A file containing the current set of refined
parameters.
The calculations may be invoked with:
platon shelxl.res
followed by clicking on the DELrefABS button on the main
PLATON option menu.
or the interactive keyboard instruction
CALC DELABS (NOCHECK)
Notes:
- The required direction cosines on shelxl.hkl should conform
with the SHELX76 style. Such a file should be made available by the data
reduction program used.
- The optional NOCHECK sub-keyword overrules the checking
of the direction cosines. This option should be used for good reasons
and with great care.
- DELABS will calculate the structure factors needed for this procedure
internally using the positional and displacement parameters given in
the '.res' file. When applicable, all anisotropic displacement
parameters are converted to U(eq)'s.
- DELABS can also handle (pseudo)-merohedral twins described with the
SHELXL TWIN/BASF mechanism.
- A DELABS run may be done (when applicable) on the reflection file
modified by SQUEEZE.
- Be aware of the fact that the use of DELABS/DIFABS as an
Empirical Absorption correction technique is considered to be
'sloppy crystallography' by some crystallographers/referees/journals.
- DELABS/DIFABS will in general 'correct' for more than just absorption.
It will take care of systematic errors related to data collection on
crystals too large for the homogeneous part of the X-Ray beam.
- In general, anisotropic thermal parameters will be less meaningfull
because their average deviation from spherical tends to be 'absorbed'
in the correction, making the heaviest atom in the structure look isotropic.
- This implementation attempts to avoid possible human errors
due to (or related with) cell transformation matrices, scaling factors,
anisotropic displacement parameter model etc.
- See also
Discussion on DIFABS
and
Louis
Farrugia's comparative absorption test
See for
EXAMPLE DATA.
ABSORPTION CORRECTION TOOLS
PLATON HOMEPAGE
27-Mar-2002 A.L.Spek