On Apr 27, 2009, at 9:20 AM, Peter Zwart wrote:
R_abs_twin observed data : 0.012
R_abs_twin calculated data : 0.300
Is R_abs_twin the same thing as Robs_twin in Lebedev, Vagin,
Murshudov. Acta Cryst. (2006). D62, 83-95 ?
And I guess I have rotational pseudo symmetry with Rcalctwin < 1/2.
Correct.
Interestingly when I run xtriage when the data is scaled into P 41 21
2 I get the following stats
R vs R statistic:
R_abs_twin = <|I1-I2|>/<|I1+I2|>
Lebedev, Vagin, Murshudov. Acta Cryst. (2006). D62, 83-95
R_abs_twin observed data : 0.012
R_abs_twin calculated data : 0.521
since r_abs_twin or r_obs_twin ~= 0, that's an indicator for perfect
twinning.
when data is scaled in P 41 21 2 and you still get twin laws, it means
your cell still has higher symmetry.
what are your unit cell parameters?
Sorry Peter
I err'd. When the data is scaled in P 41 21 2, xtriage reports the
summary twinning analysis as follows:
-------------------------------------------------------------------------------
Twinning and intensity statistics summary (acentric data):
Statistics independent of twin laws
- /<I>^2 : 1.971
- <F>^2/ : 0.792
- <|E^2-1|> : 0.731
- <|L|>, : 0.484, 0.318
Multivariate Z score L-test: 1.741
The multivariate Z score is a quality measure of the given
spread in intensities. Good to reasonable data are expected
to have a Z score lower than 3.5.
Large values can indicate twinning, but small values do not
necessarily exclude it.
No (pseudo)merohedral twin laws were found.
Patterson analyses
- Largest peak height : 5.297
(corresponding p value : 0.86379)
The largest off-origin peak in the Patterson function is 5.30% of the
height of the origin peak. No significant pseudotranslation is detected.
The results of the L-test indicate that the intensity statistics
behave as expected. No twinning is suspected.
-------------------------------------------------------------------------------
In this case, the only indicator for perfect twinning is 'Large values
can indicate twinning, but small values do not necessarily exclude
it.' ?
---------------------------------------------
Francis Reyes M.Sc.
215 UCB
University of Colorado at Boulder
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