[cctbxbb] Structure factor calculation weirdness

Nathaniel Echols nechols at lbl.gov
Fri Dec 7 07:46:22 PST 2012

On Fri, Dec 7, 2012 at 7:36 AM,  <Graeme.Winter at diamond.ac.uk> wrote:
> Some confusion here at diamond – it seems that the amplitude of F(hkl)
> depends on dmin

Yes, because it's using the FFT method, which means it first does map
sampling on a grid whose dimensions will partly depend on the
resolution.  I'm not sure if there is resolution dependence for the
scattering factors (I thought so, but I don't really know details),
but I tried using direct summation and the resolution effect

  f_calc = structure.structure_factors(
    d_min = dmin).f_calc()

For your toy example the speed difference isn't noticeable - for a
protein structure it will be considerable.


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