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Minor rewording of some definitions

  • To: Multiple recipients of list <coredmg@iucr.org>
  • Subject: Minor rewording of some definitions
  • From: Brian McMahon <bm@iucr.org>
  • Date: Tue, 4 Aug 1998 11:53:56 +0100 (BST)
A few rewordings are proposed based on suggestions from David. These are not
considered controversial, and will be accepted if there are no complaints
before the end of August.

(1) The phrase 'for estimated intensity reflections' should be dropped from a
number of R-factor definitions, thus:

data_refine_ls_R_Fsqd_factor
    _name                       '_refine_ls_R_Fsqd_factor'
    _category                    refine
    _type                        numb
    _enumeration_range           0.0:
    _definition
;              Residual factor R(Fsqd), [for estimated intensity reflections]
               calculated on the squares of the observed and calculated
               structure factors, for all reflections flagged as observed
               (see _reflns_observed_criterion) and included in the refinement.
               The reflections also satisfy the resolution limits established
               by _refine_ls_d_res_high and _refine_ls_d_res_low.

Also,

data_refine_ls_R_I_factor
    _name                       '_refine_ls_R_I_factor'
    _definition
;              Residual factor R(I) [for estimated reflection intensities,]
               for all reflections flagged as observed (see
               _reflns_observed_criterion) and included in the refinement.


And for the proposed new import from msCIF:

data_refine_ls_class_R_I_factor
    _name                      '_refine_ls_class_R_I_factor'
    _category                    refine_ls_class
    _definition
;              For each reflection class, the residual factor R(I) [for
               estimated reflection intensities,] for the reflections judged
               significantly intense (i.e. satisfying the threshold specified
               by _reflns_threshold_expression) and included in the refinement.


(2)
IDB>      Units of Fcalc:
IDB>      I note that these are specified to be in electrons throughout
IDB> the core.  This works well for x-ray diffraction, but different
IDB> units are needed for neutron diffraction.  Should we suggest that
IDB> '(for x-ray diffraction)' be added after the word 'electrons' in
IDB> these definitions?  This doesn't do much for neutron and electron
IDB> diffraction studies, but this may not be a problem.  See also
IDB> _refine_ls_F_calc_accuracy in msCIF.

The phrase (for X-ray diffraction) has been added to the word 'electrons'
(or 'electrons squared') in the definitions for data_refln_A_, data_refln_B_,
data_refln_F_, data_refln_F_squared_

I consider this as a provisional measure until I have fully reviewed our
discussions on proposals to allow other physical units or dimensions via a
new DDL term.


(3) The phrase 'which are symmetrically unique after merging' has been
changed to 'remaining after merging symmetry equivalent reflections' in the
definitions for 

data_reflns_shell_number_unique_all
    _name                      '_reflns_shell_number_unique_all'
;              The total number of measured reflections remaining after
               merging symmetry equivalent reflections for this resolution
               shell.
 
data_reflns_shell_number_unique_gt
    _name                      '_reflns_shell_number_unique_gt'
;              The total number of significantly intense reflections
               (see _reflns_threshold_expression) remaining after merging
               symmetry equivalent reflections for this resolution shell.
 
data_reflns_shell_number_unique_obs
    _name                      '_reflns_shell_number_unique_obs'
;              The total number of reflections classified as
               'observed' (see _reflns_observed_criterion) remaining after
               merging symmetry equivalent reflections for this resolution
               shell.

_______________________________________________________________________________
Brian McMahon                                             tel: +44 1244 342878
Research and Development Officer                          fax: +44 1244 314888
International Union of Crystallography                  e-mail:  bm@iucr.ac.uk
5 Abbey Square, Chester CH1 2HU, England                         bm@iucr.org

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