Tables for
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 3.7, p. 315

Section General features of the ICSD

J. A. Kaduka,b,c*

aDepartment of Chemistry, Illinois Institute of Technology, 3101 South Dearborn Street, Chicago, IL 60616, USA,bDepartment of Physics, North Central College, 131 South Loomis Street, Naperville, IL 60540, USA, and cPoly Crystallography Inc., 423 East Chicago Avenue, Naperville, IL 60540, USA
Correspondence e-mail: General features of the ICSD

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The chemical name is given in English following IUPAC rules, with the oxidation state in roman numerals. The formula upon which the name is based is calculated from all atoms with defined coordinates. Phase (polymorph) designations are given after a hyphen. Mineral names and group names are given for all entries that correspond to minerals. Details of the origin are given after a hyphen. The formula is coded as a structural formula, which provides the opportunity to search for typical structure units (such as SiO4). Such searches can be useful, but can easily miss structurally similar compounds, and should be used with caution.

The title of the publication is given in English, French or German. There can be several citations, but an author list is only given for the first reference. I have encountered truncated author lists. Authors' surnames can vary when the original publication uses a non-roman alphabet. In some cases, the first and last names of Chinese authors may be interchanged.

The Hermann–Mauguin space-group symbol is given according to the conventions of International Tables for Crystallography Volume A . If different origin choices are available, those space groups with the origin at a centre of symmetry (origin choice 2) are characterized by an additional `z', while an additional `s' is used for special origins (origin choice 1). Thus, the space group for magnetite may be reported as Fd-3mz or Fd-3ms, depending on which origin the authors used. Since all contemporary Rietveld programs use origin choice 2, care must be taken when importing coordinates.

Along with the fractional coordinates, atom identifiers are reported. These are principally running numbers and may differ from those reported by the authors. The oxidation state is given with a sign. When importing coordinates into a Rietveld program these oxidation states can influence which scattering factors are used, and so should be examined by the user. Both site multiplicities and Wyckoff positions are generated for all atoms.

The ICSD archives displacement coefficients (both isotropic and aniostropic) according to what the authors reported. Isotropic displacement coefficients can be given as either B or U values and anisotropic coefficients can be given as β, B or U values (or, in rare cases, using other conventions). Displacement coefficients imported into a Rietveld program should always be checked, as it is common for the program to interpret B as U and vice versa. Such wrong displacement coefficients can make Rietveld refinements hard to perform. There are a number of standard remarks and standard test codes; these text fields can be useful for limiting the universe of the search (such as for neutron-diffraction structures).

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