Standardization of crystal structure data as an aid to the classification of crystal structure types

Abstract

Owing to the different ways in which crystal structures may be described, isotypic compounds are often not identified as such. To remedy this situation, crystal structure data can be standardized by means of the structure tidy program. In the standardized data of isotypic structures, occupied sites have the same Wyckoff representation. This makes it possible to use the Wyckoff sequence (the letters of occupied Wyckoff sites) to classify crystal structure types. This classification is much finer than the previously used classification based on the Pearson code and is of great help if one wants to know whether a particular atom arrangement is already known. The standardization has enabled us not only to demonstrate new cases of isotypism, but also to discover structural relationships between different structure types with the same space group, for example substitution, vacancy or filled-in variants.