menucheckCIF procedure
PROC-NAME: STRDE_01PURPOSE: To check that _refine_ls_abs_structure_details is present if necessary.
PROCEDURE:
(1) For NON-CENTROSYMMETRIC structures only, _refine_ls_abs_structure_details should be present if a Flack parameter is given.
Otherwise issue ALERT B
" Alert B A value for _refine_ls_abs_structure_flack has been given, without an explanation in the _refine_ls_abs_structure_details field."
|
You have entered a value for Flack's absolute structure parameter (or
the software has automatically entered one for you because you have a
non-centrosymmetric space group).
If the absolute structure parameter is meaningless because the compound is a weak anomalous scatterer (i.e. no atom heavier than Si is present), it is best to remove the absolute structure parameter from the CIF. If the absolute structure parameter is meaningful, then you have forgotten to provide appropriate reference details under _refine_ls_abs_structure_details. For example: _refine_ls_abs_structure_details 'Flack (1983), XXXX Friedel pairs' and replace the XXXX with the actual number of Friedel pairs used in the refinement. [An easy way to determine the number of Friedel pairs is to look at the difference between the number of unique reflections used in SHELXL when a MERG2 and MERG 3 instruction is used (MERG 3 forces Friedel pairs to be merged before use).] |
Otherwise issue ALERT B
"Alert B A value for _refine_ls_abs_structure_rogers has been given, without an explanation in the _refine_ls_abs_structure_details field."
|
You have entered a value for Rogers' absolute structure parameter (or
the software has automatically entered one for you because you have a
non-centrosymmetric space group).
If the absolute structure parameter is meaningless because the compound is a weak anomalous scatterer, it is best to remove the absolute structure parameter from the CIF. If the absolute structure parameter is meaningful, then you have forgotten to provide appropriate reference details under _refine_ls_abs_structure_details. For example: _refine_ls_abs_structure_details 'Rogers (1981), XXXX Friedel pairs' and replace the XXXX with the actual number of Friedel pairs used in the refinement. [An easy way to determine the number of Friedel pairs is to look at the difference between the number of unique reflections used in SHELXL when a MERG2 and MERG 3 instruction is used (MERG 3 forces Friedel pairs to be merged before use).] Note that the use of Rogers' absolute structure parameter cannot cope with merohedral twins or cases where there is a partial mix of enantiomers. It is recommended that you refine using Flack's absolute structure parameter instead. |
