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Tool: Unit Cell

Unit Cell builds crystallographic unit cells using symmetry information from the input coordinate file (PDB or mmCIF, but not small-molecule CIF). It can regenerate the full unit cell, multiple unit cells, or only those parts defined by crystallographic symmetry or noncrystallographic symmetry. See also: Crystal Contacts, sym

The Unit Cell tool can be opened from the Higher-Order Structure section of the Tools menu and manipulated like other panels (more...). It is also implemented as the command unitcell.

The Atomic structure of interest should be chosen from the list of current atomic models. The space group, unit cell parameters, and numbers of transformation matrices (if available from the input file) are shown in the dialog. Buttons:

Option descriptions are for PDB symmetry records, but the equivalent information from mmCIF is used in the same way:

Changes in cell origin, number of cells, and/or offset can be applied by clicking the Make Copies button.


Many problems are due to information that is missing from (or incorrect within) the input file. One way to validate symmetry information is to identify steric clashes with the Crystal Contacts tool.

Unit Cell does not generate multimers defined by BIOMT matrices, but this can be done with the sym command.

ChimeraX does not read small-molecule CIF files, and Unit Cell does not handle them.

Only the following mmCIF tables are used:


UCSF Resource for Biocomputing, Visualization, and Informatics / March 2021