Hi, in our work we still sometimes encounter entirely new compounds with simple structures like rocksalt, spinel, etc. in order to convince ourselves and our readers that the materials are real, we have to fit the powder patterns - put in the atoms, refine lattice parameter(s), show that thermal parameters are reasonable, fit the peak shapes, background etc all together. In the case of spinels for example we can also refine the single atomic parameter and show that the bond lengths are reasonable. The refinements are used to decide whether sites are fully occupied and to decide the valence of the cation when multiple valence states are possible. It’s not the kind of thing that would get people really excited with the crystallographic methods, but it is necessary for convincing ourselves and others that the identification of the compound is reasonable. Is that Rietveld refinement? I don’t know so I call upon the list to say.
Kurt Get Outlook for iOS<https://aka.ms/o0ukef> ________________________________ From: rietveld_l-requ...@ill.fr <rietveld_l-requ...@ill.fr> on behalf of Matthew Rowles <rowle...@gmail.com> Sent: Sunday, January 14, 2024 11:04:25 PM To: Alan W Hewat <alan.he...@neutronoptics.com> Cc: Le Bail Armel <le-bail.ar...@orange.fr>; Rietveld_L <Rietveld_L@ill.fr> Subject: Re: Misconduct I see the core contribution of the Rietveld method as the point-wise calculation of a powder pattern. This then enables the refinement of the parameters. Yes, attributing QPA to Rietveld is incorrect; that is mainly due to Hill/Howard and Bish/Howard - I try to make it a point to differentiate this. calling PDF refinements Rietveld refinements is just plain wrong (afaik), unless you actually are moving crystallographic parameters around, in which case, the nomenclature gets fuzzy.. On Sat, 13 Jan 2024 at 14:39, Alan W Hewat <alan.he...@neutronoptics.com<mailto:alan.he...@neutronoptics.com>> wrote: The core of Rietveld refinement is REFINING the crystallographic parameters to fit the pattern. That was the great innovation. Is that done here ? To calculate various patterns to refine phase composition you necessarily need models of the crystal structures. But all refinements of powder patterns are not Rietveld Refinement. Quantitative analysis of powder samples is an important technique, and to attribute that to Rietveld is wrong. Same goes for Pair Distribution Function analysis. Calling everything "Rietveld Refinement" is not helpful, and actually hides the fundamental contribution of this technique to crystallography. ________________________________ Dr Alan Hewat, NeutronOptics Grenoble, FRANCE (from phone) alan.he...@neutronoptics.com +33.476984168 VAT:FR79499450856 http://NeutronOptics.com/hewat<https://urldefense.com/v3/__http://NeutronOptics.com/hewat__;!!IKRxdwAv5BmarQ!bR8Hzbc4csqSqmzz4jXPaN2SAqzUu0gu8WOlXtZTOx8piJSkXhgF8JUGaWkbeE_zV8sgBuOnpGnCKA$> _______________________________ On Sat, 13 Jan 2024, 07:00 Matthew Rowles, <rowle...@gmail.com<mailto:rowle...@gmail.com>> wrote: Hard disagree here. You're using crystallographic parameters to calculate the (intensities and positions of the) pattern. To me, that's the core of Rietveld refinement. You need to apply a peak shape model. Why not apply a model from which you can extract crystallite parameters? QPA can then be done on the output of a refinement, eg application of the internal standard method using the Hill /Howard algorithm. Its still a Rietveld refinement, I'm not just fitting peaks willy nilly; they're constrained by a crystal model. Matthew On Sat, 13 Jan 2024, 01:48 Alan W Hewat, <alan.he...@neutronoptics.com<mailto:alan.he...@neutronoptics.com>> wrote: Apart from the record number of atoms, phases, parameters, citations etc used to describe just 3 broad peaks, I object to this kind of refinement being called "Rietveld refinement". Luca called it "Rietveld-like" in MAUD, which was used here, but even that is wrong. The term "Rietveld refinement" should be restricted to the refinement of crystallographic parameters - cell dimensions, atom coordinates etc. and not applied to quantitative analysis of phases, particle size etc. Fitting peaks in powder patterns was done before Rietveld, who must be turning in his grave to see his name associated with this kind of thing. ________________________________ Dr Alan Hewat, NeutronOptics Grenoble, FRANCE (from phone) alan.he...@neutronoptics.com +33.476984168 VAT:FR79499450856 http://NeutronOptics.com/hewat<https://urldefense.com/v3/__http://NeutronOptics.com/hewat__;!!IKRxdwAv5BmarQ!bR8Hzbc4csqSqmzz4jXPaN2SAqzUu0gu8WOlXtZTOx8piJSkXhgF8JUGaWkbeE_zV8sgBuOnpGnCKA$> _______________________________ On Fri, 12 Jan 2024, 12:57 Le Bail Armel, <le-bail.ar...@orange.fr<mailto:le-bail.ar...@orange.fr>> wrote: Hi, A good candidate for the "worst Rietveld refinement of the year" award : https://pubpeer.com/publications/12069A6AD9D5D34F26031F34705D06<https://urldefense.com/v3/__https://pubpeer.com/publications/12069A6AD9D5D34F26031F34705D06__;!!IKRxdwAv5BmarQ!bR8Hzbc4csqSqmzz4jXPaN2SAqzUu0gu8WOlXtZTOx8piJSkXhgF8JUGaWkbeE_zV8sgBuN71xsjjg$> Even the difference pattern is totally fabricated. 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