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Re: New version (2.3) of core CIF dictionary available

  • To: coredmg@iucr.org
  • Subject: Re: New version (2.3) of core CIF dictionary available
  • From: spea@chem.uu.nl (a.l.spek)
  • Date: Thu, 16 Oct 2003 13:37:28 +0200 (CEST)
  • In-Reply-To: <20031004134127.GA17765@agate.iucr.org> from "Brian McMahon" atOct 4, 3 02:41:27 pm

	The currently available version of PLATON can handle both
old and new symmetry related datanames.


> Dear colleagues
> The core CIF dictionary (coreCIF) version 2.3 has been posted.
> Among the significant changes are the following:
> Two new categories, SPACE_GROUP and SPACE_GROUP_SYMOP have been introduced
> to provide more correct definitions of the crystallographic space group
> symmetry of a structure. These categories have been imported from the
> symmetry CIF dictionary, which is designed to provide data names required
> for a complete description of crystallographic symmetry. The existing
> categories SYMMETRY and SYMMETRY_EQUIV are formally marked as deprecated,
> and developers should begin the process of migrating to the new
> categories. (In accordance with the archival purpose of CIF, the old data
> names will be retained in the dictionary, but CIF reading software that
> needs to extract symmetry information should be designed to query both
> sets of possible names, either through hard-coding or by following the
> _related_items links in the dictionary.)
> Several new data names of the form _*_gt and _*_lt (e.g.
> _diffrn_ambient_pressure_gt), have been introduced to indicate upper
> and lower limits to the known value of an approximate physical
> quantity. These are not recommended for use in new studies, but
> provide a way formally to store such imprecise data extracted 
> from existing databases and legacy data collections.
> Three new data items, _atom_site_refinement_flags_adp,
> _atom_site_refinement_flags_occupancy and
> _atom_site_refinement_flags_posn, replace the now-deprecated
> _atom_site_refinement_flags. There are two reasons for this; the existing
> enumeration list contained single-letter codes which the definition
> claimed could be combined, in breach of the normal rules governing
> enumeration lists; and the three new items allow a more structured
> cataloguing of refinement restraints or constraints.
> Data names have been introduced for reciprocal cell lengths and angles.
> ==
> Further information is on the coreCIF page of the IUCr web site:
>     http://www.iucr.org/iucr-top/cif/cif_core/index.html
> The canonical version of the dictionary is available from
>     ftp://ftp.iucr.org/pub/cif_core_2.3.dic
> This dictionary was formally approved by COMCIFS on 19 August 2003.
> Brian McMahon
> Coordinating Secretary, COMCIFS
> _______________________________________________
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> coreDMG@iucr.org
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