Chapter 11.7 Detecting twinning by merohedry
Crystallography of biological macromolecules
Second Online Edition (2012)
Part 11. Data processing
Published Online: 14 APR 2012
© International Union of Crystallography 2006
International Tables for Crystallography
How to Cite
Yeates, T. O. and Tsai, Y. 2012. Detecting twinning by merohedry. International Tables for Crystallography. 311–316.
- Published Online: 14 APR 2012
The chapter defines various kinds of twinning and focuses on the detection and analysis of twinning by hemihedry. The perfect overlap of lattices causes distinct intensities to be added together, thereby affecting the intensity distribution as well as the apparent symmetry properties of the crystal, to a degree determined by the twin fraction. Equations are presented for identifying the presence of twinning and estimating the twin fraction from an analysis of diffraction intensities. Complicating factors, including anisotropy, pseudo-centring and local noncrystallographic symmetry, are discussed.
- twinning by hemihedry;
- twin fraction;
- merohedral twinning