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Re: Euler and AMoRe

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On Wed, 25 Nov 1998, Mark van Raaij wrote:

> If anyone has some time and interest, I would like to run a few things
> about Amore and Euler angles by them. Maybe I will seem stupid but I
> don't care anymore...
> I am trying some 'brute force' molecular replacement.
> True or false?
> Spacegroup P1:
> Model with no symmetry. I have to search alpha 0 to 180 degrees.
> Model with two-fold and putting the symmetry axis along z. I only have
> to search alpha 0 to 90 degrees?
> Model with three-fold and putting the three-fold along z. I only have to
> search alpha 0 to 60 degrees?
> Model with four-fold and putting the four-fold along z. I only have to
> search alpha 0 to 45 degrees?
> Model with five-fold and putting the five-fold along z. I only have to
> search alpha 0 to 36 degrees?
> Etc?
> And for higher symmetry spacegroups? For example a model with a
> three-fold in I222 or I212121?
> Any comments welcome!
> -- 
> Mark van Raaij (raaij@embl-grenoble.fr)
> EMBL c/o I.L.L., BP 156X, 38042 Grenoble cedex 9, France
> tel  +3347620 7269 reception  7282 office  7011 lab
> fax  +3347620 7199

I think ALL these statements are wrong in 2 respects!  First, in the Eulerian
angle convention used in AMoRe, it is the gamma angle range that is affected 
by the model symmetry (if the symmetry axis is placed along the z axis after
orthogonalisation).  The alpha range is affected by the crystal symmetry
along z only.  Of course if you use another Eulerian angle convention, such
as the one used by XPlor then things might well be different.  Second the 
range is given by 360/(order of axis), not 180/order as you suggest.

-- Ian

 Ian J. Tickle                           | Phone:  (+44) 171 631 6854
 Department of Crystallography           | Fax:    (+44) 171 631 6803
 Birkbeck College (University of London) | Email:  i.tickle@bbk.ac.uk
 Malet Street, LONDON WC1E 7HX, UK       | WWW:    http://www.cryst.bbk.ac.uk/