Re: Yet Another DETWIN

["S. Ramaswamy" <rams@Indra.bmc.uu.se>]

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Hi!

In cases like what you mention one of the good ways of determining
wheather you have de-twinned correctly and using the correct fraction
can be better obtained by looking at the Britton plot in combination with
what the Yeats method gives.  

I have a program to do this, but is still not fully CCP4 complaint (reads
1 reflection/line ASCII file and requires terminal input of cell space
group etc..).  The program does what the Yeats server does (but the matrix
is always not known since they are in a little library which is not
complete - but you can plug it in).  IT will calculate britton plots
before and after detwinning. It will also do what Andrew Leslies program
does of detwinning + calculating co-relation co-efficients.  If you are
interested e-mail me and I shall send you a copy of the program with
details of how to use it.

Rams.




On Wed, 4 Aug 1999, Kinkead Reiling wrote:

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> ***    CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html    ***
> 
> I have a mixed bag of NCS and Possible twinning and was interested in
> input from the board.
> The space group of my data is P3121, but the data will merge in P622
> with comparable Rsyms
> A molecular replacement of my dimer in P3121 reveals that the NCS two
> folds lies along a P6122 two fold at fractional height 1/12.
> 
> I have tried refining in P3121 and the R-Free hangs at 40%
> 
> Running my data on the Yeates twin server I get back
>  twin fraction of 0.440387 with and operator of -h -k l
> 
> Thus the following DETWIN output
> *********************************************************************************
> 
> Correlation coefficient (on intensities) for input data 0.986
>  Correlation coefficient after detwinning 0.348
> 
>  Number of reflections written to output file  13618
>  Number omitted because the twin mate was not observed    149
> 
>   Correlation coefficient as a function of resolution.
>     Dmin   Number    CC before     CC after
>                    detwinning    detwinning
>     8.67      309     0.974         0.036
>     6.20      836     0.981         0.185
>     5.08     1090     0.983         0.252
>     4.41     1230     0.976         0.085
>     3.95     1390     0.983         0.259
>     3.60     1507     0.982         0.218
>     3.34     1672     0.983         0.250
>     3.12     1771     0.980         0.179
>     2.95     1875     0.969         -.047
>     2.80     1938     0.951         -.272
> **********************************************************************************
> 
> So the question is what are the best ways to separate NCS symmetry in
> ones data from something such as twinning?
> And could the NCS be making the apparent twin fraction higher and thus
> the non-zero detwinned CC's?
> 
> cheers and thanks for the support
> kinkead reiling
> UCSF
> 
> 
> 

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 RAMASWAMY. S   
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