GSAS : If the refinement is not happy
The tools are there for difficult refinements, but:
- May not be easy!
- May only find problems when in the middle of the refinement
- Impurities in many and varied forms
- XRD and Neutron data are different enough
- different impurities showing up
- different systematic effects
- different volumes of sample having their effect
- Wrong spacegroup
- Non-optimum atom ordering
- Non-optimum tilt model
- Extra elements in the sample - have you used a microprobe?