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IUCr 1999 Triennial Report - Commission on Crystallographic Nomenclature

The Commission met in Seattle shortly before the Congress opened; all its other work throughout the triennium was accomplished either electronically or by 'snail-mail', with the following exception. Several members of the Sub-committee on the Nomenclature of n-Dimensional Crystallography met in person in July 1997 in Nijmegen, The Netherlands, in December 1997 in Paris, France, and in August 1997 in Geneva, Switzerland. Membership in the Commission is entirely ex officio, by virtue of a primary IUCr responsibility closely related to crystallographic nomenclature. Six new members joined the Commission following appointment either as Editor of an individual Volume of International Tables for Crystallography, as Chair of the Committee for the Maintenance of the Crystallographic Information File Standard (COMCIFS), or as Chair of the IUCr/OUP Book Series Committee. As in prior triennia, the work of the Commission was conducted primarily through the expert sub-committees and working groups it appoints. All recommendations arising thereby are reviewed by the Commission.

The Sub-committee on Atomic Displacement Parameter Nomenclature completed its 1994 charge of examining the merits of a uniform approach in reporting quantities that describe atomic displacement with a report entitled Atomic Displacement Parameter Nomenclature, which was published in Acta Cryst. (1996). A52, 770—781. Following a consideration of the inconsistent terms and symbols previously used for parameters denoting dynamic or static displacements of atoms in crystals, the report provides clear definitions for these quantities, discusses graphical representations of the Gaussian mean-square displacement matrix and the expressions used if the Gaussian approximation is inadequate, and makes recommendations for symbols and nomenclature. It, as all other Commission reports, is now fully accessible on-line at the Commission’s home page, see below.

The Sub-committee on the Nomenclature of n-Dimensional Crystallography, see Acta Cryst. (1996). A52, 91—124 for membership, completed its 1990 charge of assessing the extent to which the representational symbolism then in use may have become so non-uniform as to be unacceptably ambiguous with a report entitled Symbols for Point Group Transformations, Families, Systems and Geometric Classes (in n-Dimensions). The Commission accepted the revised report, with its unified notation and symbolism for crystallography in arbitrary dimensions, on 16 November 1998. It will appear in Acta Cryst.

J.-C. Tolédano was appointed Chair of the Working Group on Phase Transition Nomenclature in 1995 and R.S. Roth to membership in 1996 replacing R.L. Snyder who resigned; see Acta Cryst. (1996). A52, 91—124 for the remaining members. The Working Group completed its 1994 charge of studying the current multiple-choice nomenclature for naming the phases formed sequentially by a material as a function of temperature and/or pressure with a report entitled Structural Phase Transition Nomenclature, which was published in Acta Cryst. (1998). A54, 1028—1033. The resulting notation uses six separate fields to specify the essential crystallographic and physical characteristics of each phase in the sequence the first time the phase is named in a paper. Following first use it is recommended that if the phase is commonly associated with a trivial label such as a or I, then the first two fields only be used later in the paper to identify that phase; if not commonly associated with a label, then the second two fields should be used. Examples drawn from the sequence of phases formed by nine different materials are provided. After the revised report had been accepted, the Commission further charged the Working Group in 1998 with extending the recommended nomenclature to incommensurate, polytype, quasicrystal, magnetic and time-resolved phase transitions. Membership in the continued Working Group consists of J.-C. Tolédano (Chair), P.J. Brown, A.M. Glazer, R.S. Roth, R.S. Berry, R. Metselaar, D. Pandey, M. Perez-Mato and S.C. Abrahams.

A question concerning the definitions in the Commission report of 1989 entitled Definition of Symmetry Elements in Space Groups and Point Groups and another concerning Fig. 3 of the 1992 Commission report entitled Symbols for Symmetry Elements and Symmetry Operations led to the appointment of an ad hoc group consisting of H.D. Flack (Chair), Th. Hahn, H. Wondratschek and S.C. Abrahams. Following thorough examination, any corrections found necessary will be presented later as addenda to the original reports.

The Commission Observer [see Acta Cryst. (1997). A53, 822] has noted that COMCIFS was very active in the triennium, posting a modified version and then approving a new version of the core CIF dictionary, a new Powder CIF dictionary and a management group with responsibility for its development. There were no nomenclature issues in contention and cooperation with COMCIFS was harmonious.

The name of each member, the office on which ex officio membership depends, and the titles of all reports are listed on the Commission’s home page at http://www.iucr.ac.uk/iucr-top/comm/cnom/index.html through the skilful efforts of B. McMahon. The page also provides general information about the Commission, links to each member, to the full content on-line of all Commission reports, and to a valuable group of sites containing nomenclature resources of interest to crystallographers.

S.C. Abrahams, Chair

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Updated 6th June 1999

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