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What is Disorder?

Even in a crystal structure, atoms are constantly in motion and a refined structure represents the average of all the possible positions of the atom.​ Atoms can be refined over multiple sites to model this disorder.

There are various types of disorder, including:

Why is Disorder Important?

Understanding and analysing all possible disorder configurations is important in structural analysis and structural informatics​ to enhance structural understanding, enabling researchers to make knowledge-based decisions and undertake risk analyses.

How is Disorder Currently Handled in the Cambridge Structural Database?

Disorder is increasingly important in the Cambridge Structural Database (CSD) with the annual percentage of disordered structures increasing from 12% to 38% since 1980 due to improvements in the tools for resolving disorder in more complex systems. Currently, over 330,000 of structures in the CSD are disordered which is over 25% of the structures in the database.

Currently if a structure in the CSD contains disorder, then the minor occupancy sites are suppressed to leave a single representative atomic position that will then be matched against the chemical diagram.​ Suppressed atoms are not deleted; they simply take no further part in the establishment of the crystallographic connectivity and therefore will not be used in ConQuest 3D searches.​

Refcode ABATAY displayed in Mercury with the unconnected disordered suppressed atoms.

New Disorder Improvements in the CSD Portfolio

Improvements to how disorder is handled when you load a CIF into Mercury or the CSD Python API include the ability to:

It is also possible to load CIFs into enCIFer and visualize the different disorder models​.

A new disorder class has also been added to the CSD Python API which allows users to run a number of calculations on the combinations of the different disorder models.

Structure showing both the disorder models with the hydrogen bonds for each disorder model also displayed.
Structure showing the higher occupancy disorder model with the hydrogen bonds displayed for this model.
Structure showing the lower occupancy disorder model with the hydrogen bonds displayed for this model.

Future Disorder Improvements – Talk to Us!

We are excited by these new improvements to how we handle disorder in CCDC tools and we hope you find these improvements useful in your work. This is the first phase of the project and in future work we want to add disorder models to CSD entries but we would also be interested in what your priorities are in this area to guide us in the development work we do in the future – please get in touch to share your disorder insights.

Next Steps

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CSD (147)

CSD Python API (17)

Mercury (25)