Please consider the following new default values.

Tue Feb 27 22:22:48 GMT 2018

The suggested defaults I distributed earlier have now been removed from the
core dictionary.

James.

On 14 December 2017 at 02:35, Brown, David <idbrown at mcmaster.ca> wrote:

> James,
>
> These defaults should ABSLOLUTELY NOT appear in the dictionary. They were
> deliberately omitted from the original dictionaries because they are in no
> way guaranteed to be correct. Anyone looking for room temperature
> structures must know the difference between structures where the author
> states that the experiment was done at room temperature and those where the
> temperature was not given and might have had any value. It is impossible to
> do science properly if you are being fed information that you cannot rely
> on. An absorption correction may have been applied; the crystal has a high
> probability of not being white if the author fails to indicate the colour.
> There are many crystal structures reported without much of this
> information, and just because an author fails to say that he or she used Mo
> radiation does not mean they used copper. I did a study once on anisotropic
> atomic displacement parameters and had to reject most of the values
> reported in terms of B (rather than U or beta) because there are two
> conventions, and most authors did not say which convention they used. If I
> had been presented with an assumed default I would have had to reject all
> the results with the assumed value because I could not rely on its
> authenticity.
>
> If default values are needed, they should be supplied by the application
> software that reads the CIF. Presumably it has a better idea of what the
> default should be as well as the effect of that such an assumption would
> have on the subsequent use of the information. The default value should
> always be ?, meaning that nothing is known about the value. Even the
> default . (period) would be wrong, since the dictionary cannot know whether
> an item is inapplicable or just not reported.
>
> None of the suggestions in the list should be implemented. If something is
> unknown, it is, surprisingly, not known and should not be guessed at by a
> dictionary that knows nothing about the measurements, even if the
> dictionary gets it right much of the time.
>
> David
>
> I. David Brown
> Professor Emeritus
> Department of Physics and Astronomy
> McMaster University
> Hamilton, Ontario, Canada
> ------------------------------
> *From:* coreDMG [coredmg-bounces at iucr.org] on behalf of James Hester [
> jamesrhester at gmail.com]
> *Sent:* December 13, 2017 00:52
> *To:* Distribution list of the IUCr COMCIFS Core Dictionary Maintenance
> Group
> *Subject:* Please consider the following new default values.
>
> Dear Core DMG,
>
> A number of new default enumeration values were introduced in the new DDLm
> dictionary which are not present in the old DDL1 dictionary. Could you
> please consider whether or not they are reasonable and comment either here
> or at Github.  A lack of comments will lead to Antanas and I likely erring
> on the side of caution and removing those that are not obviously correct.
>
> I reproduce Antanas' list and comments below (html format). If this is
> unreadable, please view the original at https://github.com/COMCIFS/
> cif_core/issues/58.
>
> James.
> ===
>
> *1. Experimental*
> ID Data name Default
> 1.1 _exptl_crystal_density_meas_temp 293.
> 1.2 _exptl_crystal_density_meas_temp_lt 293.
> 1.3 _exptl_crystal_density_meas_temp_gt 293.
> 1.4 _exptl_crystals_number 1
> 1.5 _exptl_absorpt_correction_type none
> 1.6 _exptl_crystal_colour_primary white
>
> The _exptl_crystals_number and _exptl_absorpt_correction_type seem
> reasonable, but should
> exptl_crystal_density_meas_temp_* and_exptl_crystal_colour_primary have
> default values at all?
>
> *2. Atom sites solution*
> ID Data name Default
> 2.1 _atom_sites_solution_hydrogens difmap
> 2.2 _atom_sites_solution_primary direct
> 2.3 _atom_sites_solution_secondary difmap
>
> *3. Diffraction radiation*
> ID Data name Default
> 3.1 _diffrn_radiation_wavelength_determination fundamental
> 3.2 _diffrn_radiation_probe x-ray
> 3.3 _diffrn_radiation_xray_symbol K-L~3~
> 2.4 _diffrn_radiation_source tube
> 3.5 _diffrn_source_target Cu
>
> Note: the _diffrn_radiation_source data item has only become an
> enumerator value in the DDLm version of the dictionary. It is more
> thoroughly discussed in issue #59
> <https://github.com/COMCIFS/cif_core/issues/59>.
>
> *4. Reflections*
> ID Data name Default
> 4.1 _refln_[A|B|F|F_squared]_calc 0
> 4.2 _refln_[A|B|F|F_squared]_meas 0
> 4.3 _refln_[F|F_squared]_sigma 0
>
> *5.Diffraction reflections*
> ID Data name Default
> 5.1 _diffrn_refln_scan_mode ot
> 5.2 _diffrn_refln_scan_mode_backgd st
>
> *6.Chemical*
> ID Data name Default
> 6.1 _chemical_enantioexcess_crystal_technique CD
> 6.2 _chemical_enantioexcess_bulk_technique OA
> 6.3 _chemical_absolute_configuration .
>
> *7.Refinement*
> ID Data name Default
> 7.1 _atom_site_refinement_flags .
> 7.2 _atom_site_refinement_flags_adp .
> 7.3 _atom_site_refinement_flags_posn .
> 7.4 _atom_site_refinement_flags_occupancy .
>
> Seems reasonable since the lack of these data items imply that the related
> techniques were not applied thus resulting in a '.' (inapplicable) special
> value.
>
> *8.ADP*
> ID Data name Default
> 8.1 _atom_site_adp_type Uiso
>
> Seems reasonable.
>
> *9.Crystal system*
> ID Data name Default
> 9.1 _space_group_crystal_system triclinic
>
> This addition seems a bit strange. Might it be related to the removal of
> the default *cell_angle** values (discussed in #57
> <https://github.com/COMCIFS/cif_core/issues/57>)?
>
> *10.Bibliography*
> ID Data name Default
> 10.1 _journal_page_first 1
> 10.2 _publ_body_element section
> 10.3 _journal_index_type O
> 10.4 _citation_coordinate_linkage yes
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>
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