Hi David
No F23 has 4 alternate non-equivalent origins (i.e. invariant
amplitudes, different phases):
(0, 0, 0)
(1/4, 1/4, 1/4)
(1/2, 1/2, 1/2)
(3/4, 3/4, 3/4)
You can of course have other combinations of these by adding any of the
4 F-centring translations.
You can work this out from this table:
http://www.ccp4.ac.uk/html/cheshirecell.html
For F23 (in the list on the right, 2 lines from the bottom) you see that
the Cheshire space group is I-centred (Im3m in the 1st column) and the
Cheshire cell is (a/2, b/2, c/2). The lattice translation gives the
origin at (1/2, 1/2, 1/2) and the combination of this with the I
centring of the Cheshire SG gives the origins at (1/4, 1/4, 1/4) & (3/4,
3/4, 3/4).
HTH!
-- Ian
> -----Original Message-----
> From: [log in to unmask] [mailto:[log in to unmask]]
On
> Behalf Of David Waterman
> Sent: 06 August 2008 13:27
> To: [log in to unmask]
> Subject: translation of atom sites and maps
>
> Hi,
>
> I have a SAD dataset in F23 that I have solved using both SHELX (via
> hkl2map) and phenix, and for my own obscure reasons I want to compare
the
> results. Both SHELXD and phenix.hyss find 2 sites and both pipelines
go on
> to produce protein-like maps. I opened the heavy atom sites in Coot
and
> was surprised to find that the two sets of sites were different - that
is,
> they were not related by crystallographic symmetry. However, after
looking
> a little deeper, I found the tool phenix.emma, which told me that the
> sites were indeed related, by a translation of {0.25, 0.25, 0.25}.
>
> I must admit I'm confused about how this can be the case (I thought
there
> was only one choice of origin?), but I'd still like to compare the
> results. I can easily edit one of the pdb files of the heavy atom
sites to
> cause the required translation, however in order to translate the maps
for
> comparison in Coot I need to do something more complicated, like
rotate
> all of the phases in one of the MTZ files by a various amounts. How
can I
> change an MTZ file to result in a real space translation of the
electron
> density?
>
> Cheers
> David
>
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