andreasdrejer
Hi everyone
I am refining on some synchrotron X-ray data with an energy of approx. 60 keV (approx 0.2 Å). I get the following message (for all types of elements used in the refinement):
Invalid f1 and f11 for X in file C:\Topas-6\ssf\X.nff
for the wavelength 0.2113.
Setting value(s) to zero
The refinement looks fine, but I am in doubt when I should do anything (and how) with the anomalous form factors (f1 and f11) since I am getting this message.
I have tried to read about how TOPAS defines and uses atomic form factors in the technical reference and in the book "Rietveld Refinement - Practical Powder Diffraction Pattern Analysis Using Topas".
I here read that the anomalous form factors f1 and f11 are stored in ".nff"-files and are dependent on the energy of the X-rays used. The ".nff"-files covers a range from 10 eV to 30 keV, which means that I am far above this range.
I guess that my refinement looks fine since the values of the only the f0 term from normal scattering is used and that it only becomes a problem if I the wavelength I use is in the vicinity of an absorption edge of the elements in my sample, which as far as I know is not the case here.
I can see that it is possible to define f1 and f11 manually in the ".inp"-file or refine them, but that they are strongly correlated to scale factor, displacement parameters (which is why I am asking how to proceed if it is needed to include f1 and f11).
Best regards
Andreas
silveira
Greetings Andreas and everyone,
I have the same curiosity, since I am also using high energy synchrotron data.
By plotting the data for Fe and C (in attachment), we can see that values of f1 and f2 stabilizes, respectvely, around 6 and 0 for C and 26 and 0 for Fe.
So I would presume that for even higher energies, these values would be mantained? Therefore, I should set f1 and f11 to same values obtained at 30keV?
Best regards,
Antonio
rowlesmr
As f1 and f2 are related to absorption edges, I would approach the problem the way you have. It might break down in the 100s of keV, but should be good for most Diffraction-like energies.