RE: [EXTERNAL] Re: Misconduct/terminology

[Lind-Kovacs, Cora]

I should have been more specific – this was not with respect to QPA 
specifically – it was a more general statement about the terminology of when we 
should or shouldn’t use the expression “Rietveld refinement”.
Although we actually often do Rietveld refinements on 2 phase mixtures, where 
one phase is an internal standard, which we use to determine sample height 
offset changes with temperature.
And no, we don’t just try to get lower R-values by randomly adding parameters! 
Cora

From: Alan W Hewat 
Sent: Tuesday, January 16, 2024 11:54 AM
To: Lind-Kovacs, Cora 
Cc: rietveld_l@ill.fr
Subject: Re: [EXTERNAL] Re: Misconduct


"In many cases, we will indeed refine those structural parameters to get the 
best possible match".

The best possible match is not the objective of QPA, but rather the best 
possible estimation of the phase fractions. You can refine parameters 
describing particle size, strain, lattice constants, etc for each phase, but 
please believe the structural coordinates obtained from well characterised 
(usually mono-phase) samples.

Whether it is structure refinement or phase refinement, please resist the 
temptation to add parameters simply to obtain a lower R-factor.


Dr Alan Hewat, NeutronOptics
Grenoble, FRANCE (from phone)
alan.he...@neutronoptics.com<mailto:alan.he...@neutronoptics.com>
+33.476984168 VAT:FR79499450856
http://NeutronOptics.com/hewat<http://neutronoptics.com/hewat>
___


On Tue, 16 Jan 2024, 17:34 Lind-Kovacs, Cora, 
mailto:cora.l...@utoledo.edu>> wrote:
I like Stefan’s view outlined below. In many cases, we will indeed refine those 
structural parameters to get the best possible match. But when I use a 
structural model so that I calculate F(hkl) values, and combine that with the 
ability to vary all kinds of parameters - some structure-related, some 
instrument/setup related, some microstructure related – I would (and have!) 
call that a Rietveld refinement.
Because if I did not, there would be a lot of fun questions to contemplate: 
What if I start doing a Rietveld refinement according to the more restrictive 
definition that has been used in this discussion - and then turn off those 
structural parameters for one reason or another, maybe to look into 
hkl-dependent broadening or such (still constrained by the structure in 
contrast to simple “profile fitting” where any peak can have its completely 
independent parameters!)? Did I just quit doing a Rietveld refinement? What if 
I have a problematic atom, maybe on a split site close to an inversion center, 
and I turn that one off? Do I stop doing a Rietveld refinement when I change 
that variable to “no”? Does any Rietveld refinement start out as a 
“non-Rietveld refinement” when we adjust background, lattice parameters, 
approximate peak shapes and phase fractions, to get to a point where we can 
actually vary the structural variables without disastrous consequences? And the 
moment we touch the structural variables, in the same software, suddenly it 
becomes a Rietveld refinement? Do I need to only turn on ADPs, or is the 
“threshold” that I must allow atom positions to refine before I can call it 
Rietveld? If so, do I need to turn on all atom positions or only some of them? 
What if I define rigid bodies, do I still qualify for a Rietveld refinement?
Just some fun thoughts here! 

Cora

From: rietveld_l-requ...@ill.fr<mailto:rietveld_l-requ...@ill.fr> 
mailto:rietveld_l-requ...@ill.fr>> On Behalf Of 
Stefan Seidlmayer
Sent: Tuesday, January 16, 2024 9:51 AM
To: rietveld_l@ill.fr<mailto:rietveld_l@ill.fr>
Subject: [EXTERNAL] Re: Misconduct

Dear all,

I was following the discussion also with great interest, as terminology is 
important to distinguish properly between different items.

To my understanding the Rietveld approach was new because it constrained the 
fitting of a peak list generated "from a structure" with the refinement of the 
profile of the peaks themselves.

Thus I would have the impression that everytime when we use a constrainement of 
peak list which is generated from a structure and do not refine a list of 
"individual peaks" it is a Rietveld-type refinement.

A Profile Refinement is/was in my current understanding, when the 
peak/reflection position is not constrained by the structure parameters, but 
can be refined in an arbitrary way, individual for each peak/reflection.
From the positions refined in this way, one could then determine cell parameter 
etc. But this would require a secondary step. First refine all found 
peaks/reflection with a common profile. Then determine the lattice parameters 
from the refined peak positions etc.
This is also troublesome as without prior structure "knowledge" it may and 
surely is that certain reflection which in fact are overlapping multiple 
reflections are improperly identified as "one" reflection.
Thi

RE: [EXTERNAL] Re: Misconduct

[Lind-Kovacs, Cora]

I like Stefan’s view outlined below. In many cases, we will indeed refine those 
structural parameters to get the best possible match. But when I use a 
structural model so that I calculate F(hkl) values, and combine that with the 
ability to vary all kinds of parameters - some structure-related, some 
instrument/setup related, some microstructure related – I would (and have!) 
call that a Rietveld refinement.
Because if I did not, there would be a lot of fun questions to contemplate: 
What if I start doing a Rietveld refinement according to the more restrictive 
definition that has been used in this discussion - and then turn off those 
structural parameters for one reason or another, maybe to look into 
hkl-dependent broadening or such (still constrained by the structure in 
contrast to simple “profile fitting” where any peak can have its completely 
independent parameters!)? Did I just quit doing a Rietveld refinement? What if 
I have a problematic atom, maybe on a split site close to an inversion center, 
and I turn that one off? Do I stop doing a Rietveld refinement when I change 
that variable to “no”? Does any Rietveld refinement start out as a 
“non-Rietveld refinement” when we adjust background, lattice parameters, 
approximate peak shapes and phase fractions, to get to a point where we can 
actually vary the structural variables without disastrous consequences? And the 
moment we touch the structural variables, in the same software, suddenly it 
becomes a Rietveld refinement? Do I need to only turn on ADPs, or is the 
“threshold” that I must allow atom positions to refine before I can call it 
Rietveld? If so, do I need to turn on all atom positions or only some of them? 
What if I define rigid bodies, do I still qualify for a Rietveld refinement?
Just some fun thoughts here! 

Cora

From: rietveld_l-requ...@ill.fr  On Behalf Of Stefan 
Seidlmayer
Sent: Tuesday, January 16, 2024 9:51 AM
To: rietveld_l@ill.fr
Subject: [EXTERNAL] Re: Misconduct

Dear all,

I was following the discussion also with great interest, as terminology is 
important to distinguish properly between different items.

To my understanding the Rietveld approach was new because it constrained the 
fitting of a peak list generated "from a structure" with the refinement of the 
profile of the peaks themselves.

Thus I would have the impression that everytime when we use a constrainement of 
peak list which is generated from a structure and do not refine a list of 
"individual peaks" it is a Rietveld-type refinement.

A Profile Refinement is/was in my current understanding, when the 
peak/reflection position is not constrained by the structure parameters, but 
can be refined in an arbitrary way, individual for each peak/reflection.
From the positions refined in this way, one could then determine cell parameter 
etc. But this would require a secondary step. First refine all found 
peaks/reflection with a common profile. Then determine the lattice parameters 
from the refined peak positions etc.
This is also troublesome as without prior structure "knowledge" it may and 
surely is that certain reflection which in fact are overlapping multiple 
reflections are improperly identified as "one" reflection.
This is very the neatness of the Rietveld approach comes into play, as it 
generates even overlapping reflections which then generate the total profile by 
constraining them with the profile parameters.

So the main point in differentiation is then in my eyes:
Rietveld-Refinement: The use of a structure generated peak list which is 
constrained with profile parameters.

Profile-Refinement: Profile refinement can work on individual peaks with NO 
structure information at all.

Pawley-Refinement then is logically a little bit of a Hybrid, as the reflection 
list is pre-generated from the structure. But the intensities are just matched 
to best fit the profile. While in a true Rietveld even the reflection 
intensities is always generated from the underlying structure model applied in 
the Rietveld refinement.

What do you think of this point of view? Am I overlooking something?

Best regards

Stefan Seidlmayer



Am Di., 16. Jan. 2024 um 15:23 Uhr schrieb Alan W Hewat 
mailto:alan.he...@neutronoptics.com>>:
Ha ! When Terry Sabine proposed to call it Rietveld Refinement, I told him that 
Rietveld was already "refined".


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, 15:11 , 
mailto:alberto.martine...@spin.cnr.it>> wrote:
Dear all,

I'm following this interesting discussion. It seems to me that sometimes
there is an improper use of terminology, in particular when we talk
about "profile refinement"; in reality, we all know that it is about
"profile fitting". Or did I miss something?

Registration link for database workshop

[Lind-Kovacs, Cora]

Hello everyone,

I apologize that the registration link for the database workshop was 
accidentally excluded from the previous e-mail. The form to register is found at
https://docs.google.com/forms/d/e/1FAIpQLSezswwokQ5Yn2meCjqrlomV-8swqqQkpuUxywWLZwGiGwT2vA/viewform
Thank you,

Cora


Dr. Cora Lind-Kovacs
Professor & Associate Chair
WO 2262
Department of Chemistry & Biochemistry, MS 602
The University of Toledo
Toledo, OH 43606
phone: (419) 530-1505
fax: (419) 530-4033
e-mail: cora.l...@utoledo.edu


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Database workshop

[Lind-Kovacs, Cora]

On behalf of The U.S. National Committee for Crystallography (USNC/Cr) of the 
National Academies of Sciences, Engineering, and Medicine, I am happy to 
announce "Exploring Structural Database Use in Crystallography: Workshop 
Series", starting March 21, 2022. The workshop series is open to any interested 
attendees, including students, researchers, and early career faculty. The 
topics will focus on using, developing, and maintaining crystallographic and 
structural databases- encompassing macromolecular, small molecule, and powder 
diffraction. We will open the series with a keynote delivered by John Helliwell 
(IUCr Chair of the Committee on Data) on March 21, 2022 followed by 10 one-day 
and two-day workshops focused on 8 different structural and crystallographic 
data resources. An overview of the program can be found at the link below.

Registration for this online series is free. To read more about each session 
and to register, please visit:

https://www.nationalacademies.org/our-work/exploring-structural-database-use-in-crystallography-a-usnccr-workshop-series

The workshop is sponsored by the National Institute of Standards and Technology 
(NIST).

For more information, please contact Ana Ferreras, Telephone: (202) 334-1697 
Email: aferre...@nas.edu



Dr. Cora Lind-Kovacs
Professor & Associate Chair
WO 2262
Department of Chemistry & Biochemistry, MS 602
The University of Toledo
Toledo, OH 43606
phone: (419) 530-1505
fax: (419) 530-4033
e-mail: cora.l...@utoledo.edu


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