PDFgui does not fit for long ranges (300 Angstrom)

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ali dordaee

Jul 11, 2021, 8:17:36 AMJul 11
to diffpy-users
Dear all;
 All of the fits I have seen till now, are for a 20 or 30 Angstrom range. This range of fit is not very useful for a 300 Angstrom particle. The thing I mean, is: I want PDFgui to give me particle size for my particle. But PDFgui can not fit for this long range. The problem I face when tryin to do so, is, it does not fit at all.

 Using Diffpy-CMI I can easily get the size, but I want to know if I can do so using PDFgui. Thanks in advance.

Peter Metz

Jul 19, 2021, 9:42:14 AMJul 19
to diffpy-users
If you're interested in the structure at 30 nanometers, are you not better served by looking at the data in reciprocal space?

To fit PDF data out to 300 AA, you need (1) a quite high resolution diffractometer, and (2) a good understanding / model of resolution effects in the data (for instance, as discussed here https://doi.org/10.1107/S2053273318003224 ).

If you mean that you wish to extract a size estimate for ca. 30 nm particles, your problem is to distinguish between size damping in direct space and resolution damping, both of which are multiplicative gaussian(ish) envelopes (with a bunch of assumptions rolled in).

Perhaps I'm not reading the question correctly, but it seems that at 30 nm you've left the domain in which PDF excels, and would be better suited by a return to reciprocal space.

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