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As of 2008, more than 700,000 crystal structures have been published and stored in crystal structure databases. The publishing rate has reached more than 50,000 crystal structures per year. These numbers refer to published and republished crystal structures from experimental data. Crystal structures are republished owing to corrections for symmetry errors, improvements of lattice and atomic parameters, and differences in diffraction technique or experimental conditions.
Crystal structures are typically categorized as minerals, metals-alloys, inorganics, organics, nucleic acids, and biological macromolecules. Individual crystal structure databases cater for users in specific chemical, molecular-biological, or related disciplines by covering super- or subsets of these categories. Minerals are a subset of mostly inorganic compounds. The category ‘metals-alloys’ covers metals, alloys, and intermetallics. Metals-alloys and inorganics can be merged into ‘non-organics’. Organic compounds and biological macromolecules are separated according to molecular size. Organic salts, organometallics, and metalloproteins tend to be attributed to organics or biological macromolecules, respectively. Nucleic acids are a subset of biological macromolecules.
Comprehensiveness can refer to the number of entries in a database. On those terms, a crystal structure database can be regarded as comprehensive, if it contains a gapless collection of all (re-)published crystal structures in the category of interest and is updated frequently. Searching for structures in such a database can replace more time-consuming scanning of the open literature. Access to crystal structure databases differs widely. It can be divided into reading and writing access. Reading access rights (search, download) affect the number and range of users. Restricted reading access is often coupled with restricted usage rights. Writing access rights (upload, edit, delete), on the other hand, determine the number and range of contributors to the database. Restricted writing access is often coupled with high data integrity.
In terms of user numbers and daily access rates, comprehensive and thoroughly vetted open-access crystal structure databases naturally surpass comparable databases with more restricted access and usage rights. Independent of comprehensiveness, open-access crystal structure databases can spawn open-source software projects, such as search-analysis tools, visualization software, and derivative databases. Scientific progress can be slowed down by restricting access or usage rights as well as limiting comprehensiveness or data integrity. Restricted access or usage rights are commonly associated with commercial crystal structure databases. Lack of comprehensiveness or data integrity, on the other hand, are associated with some of the open-access crystal structure databases. Apart from that, several crystal structure databases are freely available for primarily educational purposes, in particular mineralogical databases.
Crystallographic databases can specialize in crystal structures, crystal phase identification, crystallization, crystal morphology, or various physical properties. More integrative databases combine several categories of compounds or specializations. Structures of incommensurate phases, nanocrystals, thin films on substrates, and predicted crystal structures are collected in tailored special structure databases.
Read more about this topic: Crystallographic Database
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