Twin detection with improved robustness

The twin statistic calculated here is based on local intensity differences making it less sensitive to phenomena that tend to confound traditional intensity statistics, such as anisotropic diffraction and pseudo-centering.

Reference: J. Padilla & T. O. Yeates. A statistic for local intensity differences: robustness to anisotropy and pseudo-centering and utility for detecting twinning. Acta Crystallogr. D59, 1124-30, 2003.

This twinning test was implemented with the program "dataman" available from the Uppsala Software Factory.

This is Version 3. Version 2 can be found here.

Comments and Questions on the Twinning Server may be sent to: yeates at
Please send any Problems with the website to: holton at

Perform the Twin Test on Your Data
Indicate the format of the input structure factors
CNS/X-PLOR format F and sigma(F) must be labeled "FOBS" and "SIGMA"
free format h, k, l, F, and sigma(F) read in free format
Indicate the space group
Triclinic P1
Monoclinic P2 or P21
Orthorhombic P222 or P2221 or P21212 or P212121
C222 or C2221
I222 or I212121
Trigonal P3 or P31 or P32
R3 (hexagonal)
P321 or P3121 or P3221
P312 or P3112 or P3212
Tetragonal P4 or P41 or P42 or P43 I4 or I41
P422 or P4212 or P4122 or P4222 or P4322 or P41212 or P42212 or P43212
I422 or I4122
Hexagonal P6 or P61 or P62 or P63 or P64 or P65
P622 or P6122 or P6222 or P6322 or P6422 or P6522
Cubic P23 or P213
I23 or I213
P432 or P4132 or P4232 or P4332
I432 or I4132
F432 or F4132
Perform Twinning Analysis

A plot of the twinning statistic should appear momentarily.