Crystallographic Information Resources

Crystallographic information provides the fundamental basis for understanding the properties and behavior of materials. This data, such as chemical composition, unit cell dimensions, space group, and atomic positions, derives from the primary literature that is, from published experimental measurement or theoretical calculation. Although the major crystallographic journals provide their published data in the form of computer-readable *.cif text files, finding and accessing this material directly is often difficult and certainly time-consuming. On the other hand, we are fortunate to have ready access through the Internet to extensive crystallographic databases, both academic/commercial and free, where the former databases are critically compiled and of the highest quality. The available databases generally specialize, as for inorganic or organic materials, or minerals, etc. The current paper is directed at the occasional user of crystallographic information, and examines methods of searching for and obtaining crystallographic information (mainly inorganic and minerals, but also organic, biological and metallic) from some important free databases; namely: NIMS AtomWorks for inorganics; the Crystallography Open Database (COD) for both inorganics and organics; WWW-Mincryst for minerals; the Protein Databank (PDB) for proteins and nucleic acids; and the Database of Zeolite Structures. An example of a search repeatedly used here demonstrates the changes in information provided from the first X-ray structural determination (of halite by the father-and-son Braggs) to modern representations. The professional researcher is best served by the academic/commercial databases: Inorganic Crystal Structure Database (ICSD); Cambridge Structure Database (CSD) for organics; Pearson's Crystal Data (PCD) for inorganics; Crystmet for metallic systems, etc. However, free demonstration versions of these important databases provide user introductions and, indeed, usable data for a limited range of materials. A Table provides information and rapid access details for 11 of the major crystallographic databases. This text is directed toward the search for data, but some indication is given as to how the data collected may be used.