Dear Users Forum, I’m new to the process of fitting SAXS data, and I am looking for guidance on what assumptions to make for my models. I have a set of small, probably spherical particles that assemble into micron length rectangular prism shaped structures. I have a known crystal structure from TEM images. Is it better to model the SAXS profile as a parallelepiped (and presumably miss out on the structure factor information that is present) or as spheres? If I do as spheres, is there a good way to use the crystal structure information to help the model along? When I perform a fit with spheres, I don’t seem to get the really low q behavior that I get with the parallelepiped. When I fit with the parallelepiped, the fit takes upwards of 30 minutes, and I haven’t quite been able to dial in on the parameters. The assemblies have a lot of variation in length, but not too much in width and height. Thanks for any help that you can provide, Grayson Johnson