No change in refinement after copying refined values to initial

[Arya Sukumaran]

Hello all,
I am trying to fit a PDF data using Cubic structure.
But the low r range is not fitting well. So, I am trying to fit it with low symmetry space groups.  But after copying refined values to initial value of scale factor, there is no change in the refinement. All the refined values of atomic positions remains same as the initial values. These values change if the refined value of the scale factor is not copied to the initial. I’ve noticed this behaviour with only low symmetry space groups but not with cubic structures.

Has anyone come across a similar issue, or have insights into what might be causing this?

Thank you

[Simon Billinge]

Thanks for reporting Arya.  I don't have specific suggestions here but it may suggest that the refinement is unstable.  Did you try fixing some parameters and seeing if you can get the refinement to start with fewer parameters and then gradually letting more parameters go a few at a time?

On Wed, Apr 16, 2025 at 4:41 AM Arya Sukumaran <aryasuk...@gmail.com> wrote:

Hello all, I am trying to fit a PDF data using Cubic structure. But the low r range is not fitting well. So, I am trying to fit it with low symmetry space groups. But after copying refined values to initial value of scale factor, there is no

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Simon Billinge

Professor, 

Department of Applied Physics and Applied Mathematics

Columbia University

[Arya Sukumaran]

Thank you, Dr Billinge, for the help. It is working when I gradually open a few parameters at a time.

Thank you again for the support.