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*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)**Reply-To*:*coredmg@iucr.org*

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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