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[IUCr Commission on Crystallographic Nomenclature]

IUCr 1996 Report - Commission on Crystallographic Nomenclature

The Commission met 8 August 1996 (shortly before the Seattle Congress) with ten members in attendance, including retiring members C. E. Bugg and J. H. Robertson, the latter serving as Secretary, pro tem. Membership in the Commission is entirely ex officio, by virtue of a primary IUCr responsibility closely related to crystallographic nomenclature. H. Wondratschek became a member of the Commission as a result of his appointment earlier in the year as Editor of International Tables for Crystallography, Volume H. Following appointment during the Congress, E. Arnold and M. G. Rossmann became members as Editors of Volume F, B. McMahon as an Editor of Volume G, I. D. Brown as Chair of the Committee for the Maintenance of the Crystallographic Information File Standards (COMCIFS) and P. Coppens as Chair of the IUCr/OUP Book Series Committee. In 1996, as in prior years, the work of the Commission was shared with its Subcommittees and Working Groups.

The report by the Subcommittee on Atomic Displacement Parameter Nomenclature entitled Atomic Displacement Parameter Nomenclature was published in Acta Cryst. (1996), A52, 770-781. The Report considers the confusing and inconsistent terms and symbols in current use for parameters denoting dynamic or static displacements of atoms in crystals, focusing on individual atomic anisotropic displacement parameters representing atomic motion and possible static displacive disorder. It 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. U. Shmueli translated the Report into HTML for posting on the Web. It is now accessible in full on the Commission's home page, see below.

The Subcommittee on the Nomenclature of N-Dimensional Crystallography [see Acta Cryst. (1996), A52, 91-124 for membership] has nearly reached consensus on its first report recommending symbols and nomenclature for use in point-group transformations, families, systems and geometric classes in N dimensions, in which particular attention is devoted to the need for consistency with existing nomenclature in three dimensions. The Subcommittee continues working on the nomenclature of arithmetic classes, Bravais classes and space groups.

J.-C. Toledano was elected Chair of the Working Group on Phase Transition Nomenclature during the year. R. S. Roth was elected to membership replacing R. L. Snyder who resigned [see Acta Cryst. (1996), A52, 91-124 for the remaining members]. The Working Group is considering the best nomenclature for unambiguously naming a sequence of phases formed by a material as a function of temperature or pressure.

The recommendation of the Working Group on Statistical Descriptors in Crystallography [see Acta Cryst. (1995), A51, 565-569] to replace the term `estimated standard deviation' by `standard uncertainty' has been accepted by the Commission on Journals and incorporated into the Notes for Authors published by each IUCr journal.

The Commission has established, through the efforts of B. McMahon, an attractive and informative home page accessible through the IUCr home page or directly at URL http://www.iucr.org/comm/cnom/index.html. In addition to providing general information about the Commission, the page lists all members and the titles of all Commission Reports; it also includes hypertext links to each member and to the full content of five recent Commission Reports. The Reports Statistical Descriptors in Crystallography, I and II were translated into HTML by H. D. Flack.

A. Authier has been elected Commission Observer to COMCIFS by both bodies to enhance their close cooperation on matters of nomenclature.

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Updated 14th February 1997

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