Chemical file saved in the MacroMolecular Crystallographic Information File (mmCIF) format; contains crystallographic and magnetic related information in tag-value pairs or in a loop structure, which works like a table; alternative format to the Protein Data Bank (.PDB) format.

The mmCIF format was created in order to extend the capabilities of the .CIF file format. The format is closely similar to the CIF format, but can also store magnetic space groups, which became a necessity after Harold T. Stokes and Brandon J. Campbell extended CIF dictionaries by adding magnetic related tags.