[phenixbb] calculate Fc for the whole unit cell from a Fc of a single symmetric unit.

[Ralf Grosse-Kunstleve]

Hi Ed,

On Mon, Jul 11, 2011 at 3:35 PM, Edward A. Berry <BerryE at upstate.edu> wrote:

> It seems to me there are two things that could be meant by "expand to P1"
>
> One is when data has been reduced to the Reciprocal Space
> asymmetric unit (or otherwise one asymmetric unit of a
> symmetric dataset has been obtained) and you want to expand
> it to P1 by using symmetry to generate all the
> symmetry -equivalent reflections.
>

This is what the cctbx.miller.array.expand_to_p1() method does. -- It is a
very simple algorithm once you have the list of symmetry operations.


> The other is where a full P1 dataset has been calculated from just
> one asymmetric unit of the crystal (and hence does not exhibit the
> crystallographic symmetry) and you want to generate the transform
> of the entire crystal. (I think this is how all the space-group -
> specific fft programs used to work before computers got so fast it
> was less bother to just do everything in P1 with the whole cell)
> Presumably this involves applying the real space symmetry
> operators to get n rotated (or phase-shifted for translational
> symmetry) P1 datasets and adding them vectorially.
>

 I tend to call this "symmetry summation in reciprocal space". You are
correct, this is used when we compute structure factors with the FFT method.

Ralf
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