Dear Kurt. No, refining just cell parameters doesn't qualify as Rietveld refinement :-) Certainly Hill/Howard (1987) and Bish/Howard made important contributions to QPA, but there were earlier papers eg *Werner et al (1979) * https://scripts.iucr.org/cgi-bin/paper?a18098 that you might also reference *"Quantitative analysis of multicomponent powders by full-profile refinement of Guinier-Hägg X-ray film data"* So call it QPA Profile Refinement or something similar.
The revolution of Rietveld Refinement was to refine structural parameters directly to fit the measured profile data. That broke with a long crystallographic "belief" that it was necessary to first determine "structure factors" (Bragg intensities), requiring many more parameters, with their correlations. Attributing all profile refinement to Rietveld, is not correct, and hides the importance of Rietveld Refinement, which was hotly contested and not generally accepted by the wider x-ray crystallographic community for 10+ years Sakata and Cooper (1979) An analysis of the Rietveld refinement method https://scripts.iucr.org/cgi-bin/paper?a18236 Without wanting to start another argument, look at the van Laar and Schenk historical reference list, even if you don't accept their interpretation. https://journals.iucr.org/a/issues/2018/02/00/ib5058/#BB29 Alan ________________________________ Dr Alan Hewat, NeutronOptics Grenoble, FRANCE (from phone) alan.he...@neutronoptics.com +33.476984168 VAT:FR79499450856 http://NeutronOptics.com/hewat _______________________________ On Tue, 16 Jan 2024, 09:34 Reinhard Kleeberg, < kleeb...@mineral.tu-freiberg.de> wrote: > What is Rietveld refinement? Does "Rietveld" QPA exist? > Hill & Howard (1987) titled "QPA from Neutron Powder Diffraction Data > Using the Rietveld Method" and indeed they refined all structural > parameters of their simple phases in binary mixtures, a methodical > test of the approach. > > However, the primary goal in QPA "refinement" is to reach an > acceptable fit without running into wrong scale factors. Therefore, > peak positions, profile shapes and all structural factors potentially > biasing the scale factors must be either refined or known previously. > If everything is known, just scale factors must be "refined", may be > by a linear optimization (published since the 1980ies for experimental > patterns), no "Rietveld" code is necessary. > IMHO such simple approach can work well only under very fortunate and > simple/well known circumstances. > However, in routine QPA especially of geological materials of unknown > origin (minerals with not always exactly known chemistry and > microstructure) we typically need to optimize, begining from any > published and selected structure models > - lattice parameters (always) > - profile parameters (always), often with complicated profile models > due to disorder, anisotropic line broadening, bimodal size/microstrain > distribution etc. > - most intensity relevant site occupation (Mg-Fe substitution, K > content of interlayers in micas...), sometimes constrained to lattice > parameters > - PO correction models (if necessary). > As commonly the atomic positions of minerals are often well known from > single crystal work and small deviations do not have a significant > impact on the total scale factors, the atomic coordinates are > typically fixed in QPA. As Debye-Waller factors are hard to refine > from diffraction patterns with limited angular range and for minor > components, it is necessary to fix them in routine work. This means > they must be known exactly (literature?, refined separately (if pure > material is available), or estimated. > > So Alan, is the refinement of one site occupation factor in a QPA by > using a Rietveld software enough "structure" to label such analysis as > "Rietveld QPA"? Or, is refining cell parameters an acceptable criterion? > If not, any idea for a better name? > > Greetings > > Reinhard > > > Zitat von Alan W Hewat <alan.he...@neutronoptics.com>: > > > Yes, it's Rietveld Refinement if you refine the atomic structure > > parameters. If you define the Rietveld method as simply the calculation > of > > the powder pattern, that applies to just about any powder diffraction > > study, and under values the importance of the method. > > > > But you shouldn't refine structure parameters just to get a better fit in > > QPA by Powder Profile Refinement. I don't know how often you find > entirely > > new compounds in QPA, and can determine their structure well enough to > > publish them as new compounds. > > > > The R-factor in this study is impressively low, but it is meaningless as > > Armel has shown. > > > > ________________________________ > > Dr Alan Hewat, NeutronOptics > > Grenoble, FRANCE (from phone) > > alan.he...@neutronoptics.com > > +33.476984168 VAT:FR79499450856 > > http://NeutronOptics.com/hewat > > _______________________________ > > > > > > On Mon, 15 Jan 2024, 18:01 Kurt Leinenweber, <ku...@asu.edu> wrote: > > > >> 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> > >> 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> 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> > >> 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> > 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. > >> > >> Best > >> > >> Armel > >> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > >> Please do NOT attach files to the whole list > <alan.he...@neutronoptics.com > >> > > >> Send commands to <lists...@ill.fr> eg: HELP as the subject with no body > >> text > >> The Rietveld_L list archive is on > >> http://www.mail-archive.com/rietveld_l@ill.fr/ > >> < > https://urldefense.com/v3/__http://www.mail-archive.com/rietveld_l@ill.fr/__;!!IKRxdwAv5BmarQ!bR8Hzbc4csqSqmzz4jXPaN2SAqzUu0gu8WOlXtZTOx8piJSkXhgF8JUGaWkbeE_zV8sgBuOVERBLwQ$ > > > >> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > >> > >> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > >> Please do NOT attach files to the whole list > <alan.he...@neutronoptics.com > >> > > >> Send commands to <lists...@ill.fr> eg: HELP as the subject with no body > >> text > >> The Rietveld_L list archive is on > >> http://www.mail-archive.com/rietveld_l@ill.fr/ > >> < > https://urldefense.com/v3/__http://www.mail-archive.com/rietveld_l@ill.fr/__;!!IKRxdwAv5BmarQ!bR8Hzbc4csqSqmzz4jXPaN2SAqzUu0gu8WOlXtZTOx8piJSkXhgF8JUGaWkbeE_zV8sgBuOVERBLwQ$ > > > >> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > >> > >> > > > -- > TU Bergakademie Freiberg > Dr. R. Kleeberg > Mineralogisches Labor > Brennhausgasse 14 > D-09596 Freiberg > > Tel. ++49 (0) 3731-39-3244 > Fax. ++49 (0) 3731-39-3129 > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > Please do NOT attach files to the whole list <alan.he...@neutronoptics.com > > > Send commands to <lists...@ill.fr> eg: HELP as the subject with no body > text > The Rietveld_L list archive is on > http://www.mail-archive.com/rietveld_l@ill.fr/ > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > >
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <alan.he...@neutronoptics.com> Send commands to <lists...@ill.fr> eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
