[cctbxbb] Possible contributions to the cctbx

[Luc Bourhis]

This is a spin-off from the thread about constrained hydrogen  
refinement. On the todo list of our EPSRC project, we have a few more  
items which I think would fit well in the cctbx.

1) anharmonic thermal displacements. Not only the Gram-Charlier ones  
but also about the modelling of atoms disordered over a circle or a  
line (as done in Crystals [1]).

2) multipolar scattering factors, for charge density studies.

[1] L. Schröder, D.J. Watkin, A. Cousson, R.I. Cooper, and W. Paulus.  
Crystals enhancements: refinement of atoms continuously disordered  
along a line, on a ring or on the surface of a sphere. J. Appl.  
Cryst., 37:545–550, 2004.

Best wishes,

Luc