I am trying to work out the instrument parameters refining a standard silicon (111) reference sample. I was wondering why I do see the (2 2 2) forbidden reflection at 58.9° (not visible experimentally) in the calculated pattern after importing the CIF file in GSAS, which is preventing me to obtain a good fit.
Thanks
I am posting an update about the topic for those who may be interested in this in the future. I have been contacting the GSAS developer about this issue, and they have given a very clear explanation that fixed my problem. For some reason, GSAS was putting the maximum point symmetry (setting 1) at the origin instead of the inversion center (setting 2). By using the Transform tool I did switch from (1) to (2) and now the forbidden reflection is gone.
Did you correctly assign a space group for calculation of your profile?
Yes, this is done automatically when importing a CIF file into GSAS. I was also thinking about that being the reason, but I've checked the space group of the imported phase and it comes correct ( F d -3 m for Silicon).
I am posting an update about the topic for those who may be interested in this in the future. I have been contacting the GSAS developer about this issue, and they have given a very clear explanation that fixed my problem. For some reason, GSAS was putting the maximum point symmetry (setting 1) at the origin instead of the inversion center (setting 2). By using the Transform tool I did switch from (1) to (2) and now the forbidden reflection is gone.
Pierluigi Mondelli
Excellent feedback - we always assume software to be inviolate...
Dear Mondelli,
please have a look at the attachment and see the part ''problems with the space group setting... of Si sample...'' . As I remember, you need to change the atomic positions manually (there is something wrong in software when you input .cif file aotumatically, that is why manuel correction is needed). If you use the strategy in the pdf, your peaks will well match with the experimental data, and then you can refine it. Best regards.
Pierluigi Mondelli i am having a similar issue but am struggling to find the transform tool you mention where is it found?
- Badges
- Science method
- Similar topics
- Methodology
- Crystallography
- X-ray Diffraction
- XRD Analysis