[cctbxbb] Missing gaussians for some ions?

[Ralf W. Grosse-Kunstleve]

Hi Jan,

We have the N-Gaussians for all ions that appear in the International Tables 
Volume C. You can find the source code for the compiled-in tables here:

  cctbx/eltbx/xray_scattering

> RuntimeError:  gaussian not defined for scattering_type "Y4+".

>  RuntimeError: gaussian not defined for scattering_type  "V4+".
>  RuntimeError: gaussian not defined for scattering_type "H1+".

These three do not appear in the Int. Tables. We'd need to find out what form
factors were actually used in the refinement. I see the structures are from 
1981-1993. It could be very difficult to find out for sure.

We already have an option to make the form factor lookup less strict.
The critical line is this in cctbx/xray/structure.py:

          std_lbl = eltbx.xray_scattering.get_standard_label(
            label=t_undef, exact=True, optional=True)

I think your script should run if you set exact=False, but it will
use plain Y, V, H form factors for the unknown ions. Is that good
enough for your purposes?

Ralf