CRYSTALS enhancements: asymmetric restraints Cooper, Richard I. Thorn, Andrea Watkin, David J. Chemical crystallography Crystallography Structural chemistry refinement and analysis single crystal small molecule X-ray diffraction crystal structure The traditional Waser distance restraint, the rigid-bond restraint and atomic displacement parameter (ADP) similarity restraints have an equal influence on both atoms involved in the restraint. This may be inappropriate in cases where it can reasonably be expected that the precision of the determination of the positional parameters and ADPs is not equal, e.g. towards the extremities of a librating structure or where one atom is a significantly stronger scatterer than the other. In these cases, the traditional restraint feeds information from the poorly defined atom to the better defined atom, with the possibility that its characteristics become degraded. The modified restraint described here feeds information from the better defined atom to the more poorly defined atom with minimal feedback. 2012-October text Article: post-print Published Peer reviewed Publisher's version Published born digital doi: http://dx.doi.org/10.1107/S0021889812035790 issn: 0021-8898 Oxford Research Archive internal ID: ora:6552 http://journals.iucr.org/j/ ora:6552 en http://journals.iucr.org/j/ Readers of this article may, without needing to seek permission from the IUCr: 1) save to hard disk a local copy of the article for their personal use; 2) print off one or more copies of the article for their personal use (they may not disseminate copies to third parties); 3) include brief extracts from the article or abstract, without revision or modification, in their own publications so long as the original source is acknowledged and a full bibiographic reference given. For all other uses, please see the page "Permissions requests" (http://journals.iucr.org/services/permissions.html). urn:uuid:861c1bc5-59f3-4a7a-834c-b5ff64d966d7