Notes

⁺Deceased 30 June 2003.

¹The Parthé-Gelato (1984, 1985) algorithm was selected because it is, to our knowledge, the only one that normalizes the whole structure including the atomic coordinates. Other algorithms normalize only the space-group setting and the unit-cell basis, which by themselves are not sufficient to ensure a unique Wyckoff sequence. This algorithm has been tested in several applications and has been shown to be robust, and furthermore it has been implemented in the program STRUCTURE TIDY, which includes the Wyckoff sequence as part of its output (Gelato & Parthé, 1987). The conventions used in the Parthé-Gelato algorithm differ from those adopted elsewhere in crystallography (see the discussion in Parthé & Gelato, 1984) since they are optimized to produce a robust structure normalization, while other conventions are designed for different purposes, e.g. to emphasize the physical or chemical properties of the crystal or to provide a cell descriptor that is easy to search. The space-group setting and unit-cell basis used in the Parthé-Gelato algorithm, while essential for generating a unique Wyckoff sequence, are discarded after use and do not appear explicitly in the crystalline phase identifier. They therefore do not conflict with the different space-group and unit-cell conventions adopted by the databases using the identifier.

²Available on the IUCr web page http://journals.iucr.org/a/issues/2001/05/00/es0301/index.html.