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Atomic Displacement Parameters (ADPs)

Atomic Displacement Parameters (also known as atomic vibration parameters and thermal parameters) are used to generate displacement ellipsoids. Displacement ellipsoids represent atomic motion and can be either isotropic or anisotropic. The shape and size of ADPs can be used to highlight potential errors with the data; the smaller and more spherical the ellipses for anisotropic atoms, the better the data (see Troublesome Crystal Structures: Prevention, Detection and Resolution, R. L. Harlow, J. Res. Natl. Inst. Stand. Technol., 101(3), 327, 1996).

For ellipsoids to be displayed in Mercury, it is necessary for the relevant Uequiv and Uij values to be present in the CIF or SHELX res file being read into Mercury. Uequiv and Uij values are not stored in the CSD, thus it is not possible to view ellipsoids for entries stored in or output from the CSD. CIFs obtained through the CCDC's online request form (http://www.ccdc.cam.ac.uk/products/csd/request/) may contain these data where provided by the publishing author. Currently, Uequiv and Uij values are written only to SHELX res files from Mercury.

Ellipsoids can be displayed in Mercury using the Style: drop down menu, or by going to Display in the top level menu, selecting Styles from the resultant pull-down menu and clicking on Ellipsoids. Settings for the Ellipsoids display style may be controlled using the Ellipsoid settings... window, available from the Display, Styles menu.

Relevant Program Options

Related Topics


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