Hi Arianna, The instrument broadening parameters are unique to each instrument. There was a paper published that looks at a few common instruments (Kaduk, J. and Reid, J. Powder Diffraction 26 (1) 2011, 88-93) and reports U,V,W,X,Y, asym, S/L, H/L, etc. These may be a good guideline, but your instrument should really be calibrated with a SRM.
I had a similar result to you on my instrument when refining the instrument parameters using LaB6 SRM. I achieved better fits refining first X and Y, then UVW. I think if you get large positive or negative values for these it may indicate that there is not much broadening in the Caglioti type equation, and the parameters diverge in the fit. You could play around with some dummy instrument parameters and make simulated histograms to see the difference. If you do not have a standard reference, you really can't deconvolute the instrument and sample effects. As for the difference between old and new GSAS, I would take a look in the source code, it is well commented as to what models have been incorporated and their references. Hope this helps, Nick On Tue, Feb 27, 2018 at 10:00 AM, <gsas-ii-requ...@aps.anl.gov> wrote: > Send GSAS-II mailing list submissions to > gsas-ii@mailman.aps.anl.gov > > To subscribe or unsubscribe via the World Wide Web, visit > https://mailman.aps.anl.gov/mailman/listinfo/gsas-ii > or, via email, send a message with subject or body 'help' to > gsas-ii-requ...@mailman.aps.anl.gov > > You can reach the person managing the list at > gsas-ii-ow...@mailman.aps.anl.gov > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of GSAS-II digest..." > > > Today's Topics: > > 1. instrument parameters (Arianna Lanza) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Tue, 27 Feb 2018 16:03:36 +0000 > From: Arianna Lanza <arianna.la...@iit.it> > To: "gsas-ii@mailman.aps.anl.gov" <gsas-ii@mailman.aps.anl.gov> > Subject: [GSAS-II] instrument parameters > Message-ID: <a06a772caf334efaaa50f35772a46...@iit.it> > Content-Type: text/plain; charset="iso-8859-1" > > Dear all, > > I am new to GSAS II and have no experience with old-GSAS, so forgive me > for the basic level of the questions. > > I don't fully understand the meaning of the parameters describing the > instrumental profile. > > ? What is Z? I could not find it in the old-GSAS manual. > > ? How can I judge if the U V W X Y Z are reasonable? (in case I > don't have a reference profile from a standard) And how should a well > behaved peak width plot look like? > > ? I read that U W X Y are constrained to be >= 0, while V should > be <= 0. However I have a not so badly-fitted plot where U refined to very > negative, V to very positive, W is small and negative, X is positive and Y > negative. So (i) those parameters have no constraint by default!Why not? > Can I do it with equations?; (ii) even from my na?ve understanding it looks > like a nonsense. Most likely it is because I have broad peaks and the > interplay between strain/size/etc and instrumental parameters converged to > this artificial mess. Is it possible to deconvolute the instrument > contribution from the sample contribution, in absence of a standard? > > ? SH/L is one unique parameter as opposed to 2 separate parameters > in old-GSAS, what is its meaning now, the units and/or reasonable range? > > If you can help with even partial answers or point out useful sources of > information, I will be grateful! > > Kind regards, > > > Arianna > > > > > ,_,.-'???'-.,_,.-'???'-.,_,.-'???'-.,_,,.-'???'-.,_,.-'???'-.,_, > > Arianna Lanza, PhD > > Center for Nanotechnology Innovation@NEST > Istituto Italiano di Tecnologia > Piazza San Silvestro, 12, 56127, PISA, Italy > > > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: <http://mailman.aps.anl.gov/pipermail/gsas-ii/attachments/ > 20180227/7df88e57/attachment-0001.html> > > ------------------------------ > > _______________________________________________ > GSAS-II mailing list > GSAS-II@mailman.aps.anl.gov > https://mailman.aps.anl.gov/mailman/listinfo/gsas-ii > > End of GSAS-II Digest, Vol 162, Issue 1 > *************************************** > -- Nick Weadock PhD Candidate, Materials Science California Institute of Technology 1200 E California Blvd, Pasadena, CA 91125 MC 138-78 x2520
_______________________________________________ GSAS-II mailing list GSAS-II@mailman.aps.anl.gov https://mailman.aps.anl.gov/mailman/listinfo/gsas-ii
