Dear Jiyuan,
you can use MOLREP which takes into account pseudotranslations.
Good luck!
Karsten
>
> Dear All,
>
> Recently I collected a data set to about 3.1 angstrom. Using Xtriage program, I found a pseudo
> translational symmetry on the c-axis. I noticed that overall diffraction intensity is weak for this
> dataset. I wonder if there are flaws in the crystal and I have difficulty to solve the structure using
> phaser. Has anyone seen similar cases and any comments and suggestions? Thanks!
>
> Below is some analysis results from the Xtriage.
>
> Cell 102.937, 102.937, 203.059, 90, 90, 90, P422
> -----------------------------------------------------------------------------------------
> Largest Patterson peak with length larger than 15 Angstrom
> Frac. coord. : 0.000 0.000 0.350
> Distance to origin : 71.133
> Height (origin=100) : 48.451
> p_value(height) : 8.588e-05
> ----------------------------------------------------------
> Wilson ratio and moments
> Acentric reflections
> <I^2>/<I>^2 :2.568 (untwinned: 2.000; perfect twin 1.500)
> <F>^2/<F^2> :0.728 (untwinned: 0.785; perfect twin 0.885)
> <|E^2 - 1|> :0.850 (untwinned: 0.736; perfect twin 0.541)
> Centric reflections
> <I^2>/<I>^2 :3.953 (untwinned: 3.000; perfect twin 2.000)
> <F>^2/<F^2> :0.577 (untwinned: 0.637; perfect twin 0.785)
> <|E^2 - 1|> :1.111 (untwinned: 0.968; perfect twin 0.736)
> ---------------------------------------------------------------------------------------------------
> NZ test (0<=z<1) to detect twinning and possible translational NCS
> -----------------------------------------------
> | Z | Nac_obs | Nac_theo | Nc_obs | Nc_theo |
> -----------------------------------------------
> | 0.0 | 0.000 | 0.000 | 0.000 | 0.000 |
> | 0.1 | 0.126 | 0.095 | 0.293 | 0.248 |
> | 0.2 | 0.239 | 0.181 | 0.394 | 0.345 |
> | 0.3 | 0.327 | 0.259 | 0.471 | 0.419 |
> | 0.4 | 0.401 | 0.330 | 0.521 | 0.474 |
> | 0.5 | 0.464 | 0.394 | 0.557 | 0.520 |
> | 0.6 | 0.518 | 0.451 | 0.597 | 0.561 |
> | 0.7 | 0.569 | 0.503 | 0.635 | 0.597 |
> | 0.8 | 0.613 | 0.551 | 0.660 | 0.629 |
> | 0.9 | 0.648 | 0.593 | 0.683 | 0.657 |
> | 1.0 | 0.679 | 0.632 | 0.706 | 0.683 |
> -----------------------------------------------
> | Maximum deviation acentric : 0.071 |
> | Maximum deviation centric : 0.052 |
> | |
> | <NZ(obs)-NZ(twinned)>_acentric : +0.054 |
> | <NZ(obs)-NZ(twinned)>_centric : +0.035 |
> --------------------------------------------------------------------------------------
> L test for acentric data
> using difference vectors (dh,dk,dl) of the form:
> (2hp,2kp,3lp)
> where hp, kp, and lp are random signed integers such that
> 2 <= |dh| + |dk| + |dl| <= 8
> Mean |L| :0.490 (untwinned: 0.500; perfect twin: 0.375)
> Mean L^2 :0.323 (untwinned: 0.333; perfect twin: 0.200)
> The distribution of |L| values indicates a twin fraction of
> 0.00. Note that this estimate is not as reliable as obtained
> via a Britton plot or H-test if twin laws are available.
> -------------------------------------------------------------------------------
> Twinning and intensity statistics summary (acentric data):
> Statistics independent of twin laws
> <I^2>/<I>^2 : 2.568
> <F>^2/<F^2> : 0.728
> <|E^2-1|> : 0.850
> <|L|>, <L^2>: 0.490, 0.323
> Multivariate Z score L-test: 0.686
> -------------------------------------------------------------------------------
>
> Jiyuan Ke, Ph.D.
> Research Scientist
> Van Andel Research Institute
> 333 Bostwick Ave NE
> Grand Rapids, MI 49503
>
>
-------------------------------
Karsten Niefind
University of Cologne
Department of Chemistry
Institute of Biochemistry
Otto-Fischer-Str. 12-14
D-50674 Cologne
Tel.: +49 221 470 6444
Fax: +49 221 470 3244
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