International
Tables for
Crystallography
Volume G
Definition and exchange of crystallographic data
Edited by S. R. Hall and B. McMahon

International Tables for Crystallography (2006). Vol. G, ch. 1.1, pp. 8-9

Section 1.1.11. Other extension dictionaries

S. R. Halla* and B. McMahonb

aSchool of Biomedical and Chemical Sciences, University of Western Australia, Crawley, Perth, WA 6009, Australia, and bInternational Union of Crystallography, 5 Abbey Square, Chester CH1 2HU, England
Correspondence e-mail:  syd@crystal.uwa.edu.au

1.1.11. Other extension dictionaries

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Since the introduction of the major CIF dictionaries, several other compendia of data names suitable for describing different applications or disciplines within crystallography have been developed. Four of these are described in the current volume.

The powder CIF dictionary (pdCIF; Chapter 3.3[link] ) is a supplement to the core dictionary addressing the needs of powder diffractionists. The structural model derived from powder work is familiar to single-crystal small-molecule or inorganic scientists. However, the powder CIF effort had the additional goals of documenting and archiving experimental data. It was always intended that powder CIF be used for communication of completed studies and for data exchange between laboratories. This is frequently done at shared diffraction facilities such as neutron and synchrotron sources. The powder dictionary was written with data from conventional X-ray diffractometers and from synchrotron, continuous-wavelength neutron, time-of-flight neutron and energy-dispersive X-ray instruments in mind.

The modulated-structures dictionary (msCIF; Chapter 3.4[link] ) is also considered as a supplement to the core dictionary and is designed to permit the description of incommensurately modulated crystal structures. The project was sponsored by the IUCr Commission on Aperiodic Crystals and was developed in parallel with a standard for the reporting of such structures in the literature (Chapuis et al., 1997[link]).

A small dictionary of terms for reporting accurate electron densities in crystals (rhoCIF; Chapter 3.5[link] ) has recently been published as a further supplement to the core dictionary. It has been developed under the sponsorship of the IUCr Commission on Charge, Spin and Momentum Densities.

The symmetry dictionary (symCIF; Chapter 3.8[link] ) was developed under the direct sponsorship of COMCIFS with the objective of producing a rigorous set of definitions suitable for the description of crystallographic symmetry. Following its publication, several data names from the symCIF dictionary were incorporated in the latest version of the core dictionary to replace the original informal definitions relating to symmetry. The symCIF dictionary contains most of the data names that would be needed to tabulate space-group-symmetry relationships in the manner of International Tables for Crystallography Volume A (2005[link]). It is intended to expand the dictionary to include group–subgroup relations in a later version.

Other dictionaries are also under development, often under the supervision of one of the Commissions of the International Union of Crystallography.

Mention should also be made of the use of STAR Files by the BioMagResBank group at the University of Wisconsin to record NMR structures. This work (Ulrich et al., 1998[link]) endeavours to be complementary to the mmCIF descriptions of structures in the Protein Data Bank.

References

International Tables for Crystallography (2005). Volume A, Space-group symmetry, edited by Th. Hahn. Heidelberg: Springer.
Chapuis, G., Farkas-Jahnke, M., Pérez-Mato, J. M., Senechal, M., Steurer, W., Janot, C., Pandey, D. & Yamamoto, A. (1997). Checklist for the description of incommensurate modulated crystal structures. Report of the International Union of Crystallography Commission on Aperiodic Crystals. Acta Cryst. A53, 95–100.
Ulrich, E. L. et al. (1998). XVIIth Intl Conf. Magn. Res. Biol. Systems. Tokyo, Japan.








































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