difficulties in fitting polydisperse systems

[avalerio]

Hello,

I'm new user of Gnom/Atsas and I've have SAXS data of CeO₂ powder nanocubes that I want to fit. From images of TEM/SEM I know that the particles are polydispersed and highly aggregated. I have looked into another posts in this forum searching for fits with cubic particles, but in one specific topic I saw that there wasn't much difference in fitting for "polydisperse spheres" and "arbitrary polydisperse" options in SAS data analysis program. However, when I set the option "polydisperse spheres" I mannualy change the parameters Rmin, Rmax, etc, but most of the times I get the error message "An error occurred while running 'datporod'. ". Also the button "Autognom" is non-clickabel, which I think it prevents the program to fit the curve automatically. I was wondering if anyone could inform where to find tutorials to fit with polydisperse spheres and why I keep getting error messages. I appreciate any help and I hope I wasn't been too inconvenient.

[Guðmundsdóttir]

Probably you shouldn't fit data from cubic particles with a polydisperse mixture of spheres. And probably using GNOM doesn't make sense if the sample is highly aggregated.
Anyway, 'Autognom' should be disabled for any System that is not monodisperse, this is normal.
For an 'Arbitrary Polydisperse' system you need to provide a form factor file (sorry, never used that one).