[RMCProfile-users] Amorphous X-ray PDF fitting

Benjamin Kyffin b.kyffin at surrey.ac.uk
Mon Sep 16 15:04:15 BST 2019

Dear all,

I am working on fitting some X-ray PDF data for some amorphous materials, and I have some questions.

  1.  There was a post in 2014 about a very similar topic and at the time it was not really possible to fit XRAY_REAL_SPACE_DATA with a work around treating it as neutron data, changing the scattering length and the NEUTRON_COEFFICIENTS accordingly. Is this still the case or does fitting G(r) X-ray data work with the XRAY_REAL_SPACE_DATA command now?
  2.  I am attempting to create an amorphous model with the correct composition for my material. I have read that this is very hard to do and you can either start from a completely random box (with constraints on minimum pair distances) or a crystal structure and hope disorder is introduced during fitting. Both of these methods seem to have drawbacks. Is there a way to start from a random box of tetrahedra rather than free atoms? Or even constraints on maximum pair distances/coordination numbers?
  3.  Whilst fitting XRAY_RECIPROCAL_SPACE_DATA is it necessary to provide RECIPROCAL_SPACE_FIT/RECIPROCAL_SPACE_PARAMETERS/REAL_SPACE_FIT/REAL_SPACE_PARAMETERS? And if so what do the numbers after this parameters actually refer to?

Thanks for any help,

Ben Kyffin
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