The Merohedral Crystal Twinning Server

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Todd Yeates and Barry Fam
UCLA Department of Chemistry and Biochemistry and
UCLA-DOE Laboratory of Structural Biology and Molecular Medicine

Reference T. O. Yeates, Methods Enzymol. 276, 344-358, 1997.


TWINNING TEST

For more information on both types of twinning the please see the Introduction to Hemihedral Twinning

Perfect Merohedral Twinning Test
Perfect Merohedral Twinning involves a crystal with a twin fraction equal to or near 1/2. This test will attempt to determine the presence of twinning by comparing the diffraction data to that expected by Wilson statistics.

Partial Merohedral Twinning Test
Partial Merohedral Twinning involves twinning with a twin fraction not equal to 1/2. This test will attempt to estimate the twin fraction alpha statistically.

OPTIONS
- Resolution Limits
Output Format (Perfect Twinning Test Only)
The Perfect Merohedral Twinning Test partitions reflection data by resolution and performs independent calculations on the individual shells. The results may therefore be output in graphical (Postscript) format, or in plain text.
Reflection Discard Fraction (Partial Twinning Test Only)
The Partial Merohedral Twinning Test utilizes a statistical comparison of twin-law-related reflection pairs. Without loss of validity, the specified percentage of these pairs are discarded based upon the sum of their intensities in order to minimize statistical error.
FILE SUBMISSION
Please select a data file to upload:
Data File Format
The XPLOR format assumes records of the following form:
...
INDEX    0   1 -13 FOBS     285.27
INDEX    0   1 -10 FOBS     495.87
INDEX    0   1  -7 FOBS     306.33
INDEX    0   1  -4 FOBS     375.55
...

Only accepts XPLOR format
ADDITIONAL INFORMATION
Unit Cell Dimensions
( a , b , c ) = ( , , )

( alpha , beta , gamma ) = ( , , )

Apparent Space Group
P1

P2
P21
C2

P21212
P212121
C222
C2221
F222
I212121
I222
P222
P2221

P4
P41
P42
P43
I4
I41

P4212
P41212
P4122
P422
P42212
P4222
I422
I4122

P3
P31
P32
R3 (hexagonal)

P3121
P321
P3221
R32 (hexagonal)

P3112
P312
P3212

R3 (rhombohedral)

R32 (rhombohedral)

P6
P61
P62
P63
P64
P65

P622
P6122
P6222
P6322
P6422
P6522

F23
I213
I23
P213
P23

F4132
F432
I4132
I432
P4132
P4232
P432
P43212
P4322
P4332

CONFIRMATION
Please verify all your settings and click the submission button below to upload your data file and perform the twinning test. Depending on your internet connection, abnormally large data files may cause a delay in upload time. The test itself normally does not take more than a few seconds. If you have selected Postscript output you may need to save the results to disk and open this file with an external viewing program.


The server requires only a few seconds to return a result. If your submission takes minutes or does not return, or you get an error message of any kind, please feel free to contact the administrator.


Comments and Questions on the Merohedral Twinning Server may be sent to yeates@mbi.ucla.edu
Please send any Problems with the website to holton@mbi.ucla.edu