International
Tables for Crystallography Volume F Crystallography of biological macromolecules Edited by M. G. Rossmann and E. Arnold © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. F. ch. 24.3, p. 664
Section 24.3.2.5. 3D crystal structure data^{a}Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, England |
The three-dimensional data consist of the fractional coordinates and symmetry operators for each entry. This information, together with the cell dimensions, is used to establish a crystallographic connectivity using standard covalent radii. The chemical and crystallographic connectivities are then mapped onto one another, using graph-theoretic algorithms, so that the chemical atom and bond properties are associated with the three-dimensional structure for search purposes. The CSD always records coordinates for complete molecules. Thus, if a molecule adopts a special position in the assigned space group, i.e. the asymmetric unit is some fraction of the total number of atoms in the molecule, then the CSD system also records those symmetry-generated atoms that complete the chemical entity. This speeds up the search process and also makes the data more accessible to non-crystallographers.