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Acta Cryst. (1991). A47, 655-685

CIF standard codes

It is particularly important that certain data items be specified in a CIF as standard codes. These codes aid in the simple and unambiguous interpretation of a data item, and should be used wherever applicable. For example, the data item which describes the method by which hydrogen atoms are treated in the least-squares refinement process is associated with the data name _refine_ls_hydrogen_treatment and is assigned the CIF standard codes:

refined all H parameters
refined H coordinates only
refined H U's only
no refinement of H parameters

If an assigned CIF standard code is inappropriate, it is normal practice to add a text field of the type *_special_details. A complete list of the currently defined CIF data names with standard codes is given in Section 3 of Appendix I.

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