Modulated and composite structures dictionary (msCIF) version 1.0.1
This category description does NOT introduce a new category; instead, it describes the recommended practice for using block codes as described in the core AUDIT_LINK category for descriptions of modulated structures. The value of _audit_block_code may be associated with a data block in the same file or in a different file related to the current data block. The value of _audit_block_code should be unique. It is recommended that data blocks are named as follows: <string> The name of the data block containing those items that, for a particular material, are independent of the specific structure (modulated, reference etc.). For example, the experimental set-up or publication details would be described here. <string>_REFRNCE The name of the data block that contains specific details of the reference (unmodulated) structure if it was refined separately using only main reflections. In the case of composites, this data block may contain those items that are common to the reference structures of all subsystems. <string>_MOD The name of the data block in which specific details of the modulated structure are given. In the case of composites, this data block may include either those items that are common to the modulated structures of all subsystems or the whole modulated structure if it is described implicitly through the *_subsystem_code pointers. A trailing code following the reserved words MOD or REFRNCE indicates that the corresponding data block includes structural information corresponding to the modulated or reference structures of the subsystem labelled by _cell_subsystem_code. A recommended format for <string> is given in the definitions of _pd_block_[pd] and _pd_block_id in the dictionary extension cif_pd.dic (http://www.iucr.org/cif/pd/index.html).Examples:
Example 1 - example file for the one-dimensional incommensurately
modulated structure of K~2~SeO~4~.
loop_ _audit_link_block_code _audit_link_block_description . 'publication details' K2SEO4_COM 'experimental data common to ref./mod. structures' K2SEO4_REFRNCE 'reference structure' K2SEO4_MOD 'modulated structure'
Example 2 - example with a trailing string referencing a modulated
structure of the subsystem labelled by _cell_subsystem_code.