[ccp4bb]: Tetragonal Twinning & Detwin - Summary #1 and story so far!!

[David Briggs <d.briggs@mail.cryst.bbk.ac.uk>]

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Dear all....

	First I must thank those of you who have replied so far for you
help.. but I still have doubts... I will try and clear this up...

Roman
> However, if you are lucky and the NCS axes do not run parallel to the
> crystallographic axes, you should then be able to differentiate between
> NCS and pseudo-crystallographic two-fold axes (caused by perfect
> twinning) by examination of the self rotation function.
Unfortunately, I am not that lucky!!!
I have 2mols per asu in p422 (therefore 4 in p4). (everything SHOULD fit)
My NCS two fold does run parallel to my crystallographic axes, as I have
rather nice looking pseudo-translations peaks on my native patterson...

Bart
> Take a look at your TRUNCATE (there it is again) output to see if your
> intensity (or better E-value) distributions are normal or not. If they
> indicate twinning then I fear you do have a problem.

I have put both Intensitiy distributions and 1st and 3rd moments graphs
for p4 and p422 data on the web at...

http://student.cryst.bbk.ac.uk/~ebrig02/twin/

see what you think....
(I think I'm getting conflicting answers again!!)

Jacqui
The Detwin program indicated a near perfect twin for the p4 scaled data.
As there are no twinning operators for p422, I could not use detwin on
this data.
The UCLA twinning server, allows you to detect presence of a perfect twin
using your higher space group (for me, P422) The perfect twin test gave a
resounding "NO, you are not twinned!". However, the partial twin test
using p4 data gave a "yes, you are greater that 45% twinned" answer.

Which is right!!!

	Yours

		Confused of Birkbeck....


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