Constraints & Restraints
Yes. You can use any and all standard tools when modelling a structure – with or without NoSpherA2. All restraints and constraints that are supported during ‘normal’ refinement with olex2.refine are also supported when using non-spherical form factors. Remember: except for not using ancient spherical form factors, we are using sophisticated custom-made form factors, but otherwise everything stays the same and we use the same number of parameters.
The most common constraint you will need to use when refining with NoSpherA2 concerns the way hydrogen atoms are treated. In many cases – and especially when the underlying data is of high quality – all hydrogen atoms can be refined freely. But sometimes they can not, especially in disordered structures.
We suggest that you refine those hydrogen atoms freely that you can refine freely, and use the riding constraint for those that you can not refine freely. Extremely usefull in this context: -RefineHDist (Keep (selected) hydrogen atoms in geometry according to their IAM AFIX instruction, but refine the distane freely) -NeutronHDist (change the distance for Hydrogen atoms to values proposed by Allen and Bruno in Acta Cryst. 2010, B66, 380-386.)