Re: Rietveld website cancelled ?

[Alan Hewat]

Thanks Armel. Have a look also at the s-triazine paper. 30 years ago Pawley
and I were determining  structures of materials that are liquid at room
temperature. I remember he was worried about liquid HCN on the French
train. You might try that :-)

>From my mobile phone:
Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
 +33.476.98.41.68
http://www.NeutronOptics.com/hewat

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Re: Rietveld website cancelled ?

[Le Bail Armel]

 

>For Armel, here are a couple of examples of automatic indexing, search-match 
>and structure DETERMINATION from neutron powder data.

 

OK, let us make a 2018 analysis of 
Pawley & Hewat (1985) Acta Ctyst. B41, 136-130.
according to 2002 criteria


sample : CF3Cl = strong chemical information

Neutron : D1A (ILL) lamda = 2.98 A

Indexing : Visser (1969) : orthorhombic cell

C-centered from systematic absences

estimation of 4 molecules per cell

A packing-analysis program written to investigate CF3Cl in Cmc21
two variables needed :
translation of the molecule along y and rotation in the yz plane

Unit cell refined using the ALLHKL (Pawley, 1981) program

Final full refinement by EDINP (Pawley, 1980)

All this fits well into the SDPD 2002 maze
http://www.cristal.org/CAC-XX/Hewat-maze.jpg

You had Pawley with you...
His packing-analysis software can be considered as a precursor
of what is called nowadays the direct-space approach, rotating
and translating a known molecule (using a grid-search approach
I presume in that case) till obtaining a good fit.

A pity that he has not solved his 1981 example for his Pawley method
(decafluorocyclohex-1-ene, C6F10) using that software (was a bit
more complex).

So, this 1985 SDPD paper cannot be considered as a good example for
a confirmation of the "structure determined by the Rietveld method"
approach. but sure it is a nice structure DETERMINATION from neutron

powder data.

 


Best

Armel

 

 

 

 

> Message du 29/08/18 12:33
> De : "Alan Hewat" 
> A : "Armel Le Bail" 
> Copie à : "rietveld_l@ill.fr" 
> Objet : Re: Rietveld website cancelled ?
> 
>
> A clear distinction having my complete agreement. (Armel)
Ouf. Nous sommes d'accord enfin :-) For Armel, here are a couple of examples of 
automatic indexing, search-match and structure DETERMINATION from neutron 
powder data. Very few citations though; crystallographers largely ignored 
neutron powder diffraction before 1987 and Hi-Tc :-)


__
>
   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE 
+33.476.98.41.68
>         http://www.NeutronOptics.com/hewat
> __



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Re: Rietveld website cancelled ?

[Le Bail Armel]

 

The Hugo Rietveld crucifixion is off limits. If it is not here that we can 
discuss of it, then where ?

Contrarily to you I find a good fit with religion. And vL did not use blank 
shots.

 

Armel

 

 

 

> Message du 30/08/18 13:48
> De : "Alan Hewat" 
> A : "rietveld_l@ill.fr" 
> Copie à : 
> Objet : Re: Rietveld website cancelled ?
> 
>

> You dig !
Please stop digging Armel. Loaded guns, grave digging and religion are off 
limits.


__
>
   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE 
+33.476.98.41.68
>         http://www.NeutronOptics.com/hewat
> __








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Re: Rietveld website cancelled ?

[Alan Hewat]

> You dig !
Please stop digging Armel. Loaded guns, grave digging and religion are off
limits.
__
*   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE *
 +33.476.98.41.68
http://www.NeutronOptics.com/hewat
__
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Re: Rietveld website cancelled ?

[Le Bail Armel]

Hi,

 

>It all depends on the definition


I know since a long time that it is risky to appear discussing on that 
list containing so many gurus of the Rietveld god (christened in 1978 
by Sabine and Young ; almost nobelized in 1995 ; crucified in 2018 by 
van Laar and Schenk). If god has said that his method could "determine" 
a structure, then all gurus must agree and defend the point.

But the world has changed a lot. Indeed, structure determination from
powder diffraction data has become possible. New gods appeared 30 years
ago. Rietveld is the central god in the process according to the SDPD 
maze :  http://www.cristal.org/CAC-XX/maze.jpg
However, when the SDPD whole process is described linearly, the Rietveld 
method place is not central, it is the ultimate thing to do.

Central or ultimate, this is enough apparently for the Rietveld gurus
to tell that there is only one god, their god. Then this strange 
"refinement=determination" law in their bible.

You dig !

Armel

PS - Anyway, I will continue to do my best for a resurrection, since I
recognize being one of his sons.

 

 

 

 

> Message du 29/08/18 19:00
> De : "Peter Y. Zavalij" 

> A : "% MailingList Rietveld" 
> Copie à : elb...@jhu.edu
> Objet : Re: Rietveld website cancelled ?
> 
>

It all depends on the definition. If/when we agree on the definition, there is 
usually no points for further arguing.
Anyway we could call Relieved method a structure determination from powder data 
as long as it does not included solving structure (or as David elegantly put - 
true structural solution).
Peter









Peter Y. Zavalij
Director - X-ray Crystallographic Center
University of Maryland, 
College Park, MD 20742
> 

>










>

>

On Wed, Aug 29, 2018 at 12:38 PM David Elbert  wrote:
>

Absolutely important that people understand that the Rietveld method is 
structure refinement and not solution, but as Larry points out sometimes you 
can get a more out of it if you’re clever… and have no other choice!   Here’s a 
second example:  

>
Stubbs et al., 2010, Uranyl phosphate sheet reconstruction during dehydration 
of metatorbernite [Cu(UO2)2(PO4)2·8H2O], American Mineralogist 95 (8-9): 
1132-1140 which is a bit of a brute-force approach to implying structures of 
some uranyl phosphates in a synchrotron heating experiment.  Joanne Stubbs 
sorted through known structures of related materials and used observed trends 
in refinements to select similar structures to further investigate.  Able to 
then postulate reasonable structures which then refined to the observed data 
and provided insight into this interesting group of materials.

>
Not the standard way to employment of Rietveld Refinement and certainly not 
true structural solutions, but a smart, useful, and rather satisfying 
application nonetheless.

>
Best-
David
>

>





David Elbert
> Hopkins Extreme Materials Institute
Malone Hall
> Johns Hopkins University
> 3400 N. Charles St
> Baltimore, MD 21218
> 
> (410) 516-5049
> 
> elb...@jhu.edu
> 
>

> 
> 
> 
> 
> 
>





>


On Aug 29, 2018, at 12:09 PM, Larry Finger  wrote:


On 08/29/2018 04:15 AM, Le Bail Armel wrote:
>
Hi,
> After the IUCr Monograph on Crystallography 13 (2002)
> entitled "Stucture Determination from Powder Diffraction Data"
> you may find in the preface :
> "Although the Rietveld method of structure refinement from powder
> diffraction data is often loosely considered to be synonymous with structure
> determination, it is not. The Rietveld method only comes into play in the
> final stage of the structure solution process when an approximate structural
> model has been found."
> WIF David, K Shankland, LB McCusker, C Baerlocher
> A clear distinction having my complete agreement.
> Armel
>

> Armel,
> 
> Although the above statement may be generally true, I can provide a counter 
> example. In Max W. Schmidt, Larry W. Finger, Ross J. Angel, and Robert E. 
> Dinnabier, "Synthesis, crystal structure, and phase relations of AlSiO2OH, a 
> high pressure hydrous phase", American Mineralogist, V. 83, 881-888, 1998, we 
> only had a powder - no single crystals. From data measured at ESRF, we used 
> GSAS to isolate the peaks of interest for the unknown phase, and used program 
> TREOR to autoindex the unknown and identify the impurity phases. We then 
> extracted intensities using the LeBail method, and determined the structure 
> using direct methods with program SIRPOW. The structure was then refined with 
> GSAS. We were even able to locate the H atom from Fourier maps!
> 
> Even 20 years ago, it was possible to determine the structure from X-ray 
> powder patterns.
> 
> Larry

RE: Rietveld website cancelled ?

[Le Bail Armel]

Hi Bob,

 

A kind of unique case isn't it ?

How many of such extreme examples can you list 18 years after it ? OK, some 
papers by Margiolaki, et al...

 

But the question was :

 

>As a long time practitioner of powder XRD (since 1972) I was there when the 
>superconductor craze hit in the mid-1980s.  At that time it was recognized the 
>Rietveld Method was useful only for REFINING structures which were generally 
>accepted from single crystal x-ray analysis.

>The http://www.cristal.org/rietv025/ link says the method "[allows] an 
>accurate determination of the structure."  I take that statement to mean no 
>model is required; Rietveld Analysis can determine structure without 
>preconceived model.

 

i.e. a good crystallographer, when reading "determination" thinks that no model 
is required. Then telling that the (Rietveld) method allows an accurate 
determination of the structure is misleading since that method only allows for 
a structure refinement.

 

So, a comment such as yours seems extremely out of the subject.

"a protein structure (a new insulin phase) was solved by rigid body Rietveld 
refinement"

This is a too short and strange way to present the thing. You indexed the 
pattern, guessed a model from what was already known about insulin, and had the 
chance it was good enough for the Rietveld refinement convergence. The 
determination did not included exclusively the Rietveld method, but also your 
mind and a lot of chance- congratulations.

 

You dig.

 

Armel

 

 

> Message du 29/08/18 18:26
> De : "Von Dreele, Robert B." 
> A : "Larry Finger" , "Le Bail Armel" , "Toby, Brian H." 
> Copie à : "Rietveld_L@ill.fr" 
> Objet : RE: Rietveld website cancelled ?
> 
> Hi Armel,
> A more extreme example was in Acta D56, 1549-1533 (2000) where a protein 
> structure (a new insulin phase) was solved by rigid body Rietveld refinement 
> from a synchrotron powder data set & subsequently confirmed by a single 
> crystal analysis (see Acta Cryst. (2001). D57, 1091-1100). NB: this kind of 
> thing has also happened more recently (see papers by Margiolaki, et al).
> Bob Von Dreele
> 
> -Original Message-
> From: rietveld_l-requ...@ill.fr  On Behalf Of Larry Finger
> Sent: Wednesday, August 29, 2018 11:10 AM
> To: Le Bail Armel ; Rietveld_L@ill.fr
> Subject: Re: Rietveld website cancelled ?
> 
> On 08/29/2018 04:15 AM, Le Bail Armel wrote:
> > Hi,
> > 
> > After the IUCr Monograph on Crystallography 13 (2002)
> > 
> > entitled "Stucture Determination from Powder Diffraction Data"
> > 
> > you may find in the preface :
> > 
> > "Although the Rietveld method of structure refinement from powder
> > 
> > diffraction data is often loosely considered to be synonymous with 
> > structure
> > 
> > determination, it is not. The Rietveld method only comes into play in 
> > the
> > 
> > final stage of the structure solution process when an approximate 
> > structural
> > 
> > model has been found."
> > 
> > WIF David, K Shankland, LB McCusker, C Baerlocher
> > 
> > A clear distinction having my complete agreement.
> > 
> > Armel
> 
> Armel,
> 
> Although the above statement may be generally true, I can provide a counter 
> example. In Max W. Schmidt, Larry W. Finger, Ross J. Angel, and Robert E. 
> Dinnabier, "Synthesis, crystal structure, and phase relations of AlSiO2OH, a 
> high pressure hydrous phase", American Mineralogist, V. 83, 881-888, 1998, we 
> only had a powder - no single crystals. From data measured at ESRF, we used 
> GSAS to isolate the peaks of interest for the unknown phase, and used program 
> TREOR to autoindex the unknown and identify the impurity phases. We then 
> extracted intensities using the LeBail method, and determined the structure 
> using direct methods with program SIRPOW. The structure was then refined with 
> GSAS. We were even able to locate the H atom from Fourier maps!
> 
> Even 20 years ago, it was possible to determine the structure from X-ray 
> powder patterns.
> 
> Larry
> 
> 
>++
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++

Re: Rietveld website cancelled ?

[Kurt Leinenweber]

Was that Clint Eastwood?  - Kurt


From: rietveld_l-requ...@ill.fr  on behalf of Le 
Bail Armel 
Sent: Wednesday, August 29, 2018 12:01:25 PM
To: Rietveld_L@ill.fr
Subject: Re: Rietveld website cancelled ?


OK, seems that the SDPD book preface looks unclear to some.



Western movies adepts well know that sentence :

"You see, in this world there's two kinds of people, my friend: those with 
loaded guns, and those who dig. You dig. .."



Similarly, there are two kinds of people, those believing that the sense of the 
words "structure determination" and

"structure refinement" are the same, and the others. You dig.



Best



Armel









> Message du 29/08/18 18:09
> De : "Larry Finger" 
> A : "Le Bail Armel" , Rietveld_L@ill.fr
> Copie à :
> Objet : Re: Rietveld website cancelled ?
>
> On 08/29/2018 04:15 AM, Le Bail Armel wrote:
> > Hi,
> >
> > After the IUCr Monograph on Crystallography 13 (2002)
> >
> > entitled "Stucture Determination from Powder Diffraction Data"
> >
> > you may find in the preface :
> >
> > "Although the Rietveld method of structure refinement from powder
> >
> > diffraction data is often loosely considered to be synonymous with structure
> >
> > determination, it is not. The Rietveld method only comes into play in the
> >
> > final stage of the structure solution process when an approximate structural
> >
> > model has been found."
> >
> > WIF David, K Shankland, LB McCusker, C Baerlocher
> >
> > A clear distinction having my complete agreement.
> >
> > Armel
>
> Armel,
>
> Although the above statement may be generally true, I can provide a counter
> example. In Max W. Schmidt, Larry W. Finger, Ross J. Angel, and Robert E.
> Dinnabier, "Synthesis, crystal structure, and phase relations of AlSiO2OH, a
> high pressure hydrous phase", American Mineralogist, V. 83, 881-888, 1998, we
> only had a powder - no single crystals. From data measured at ESRF, we used 
> GSAS
> to isolate the peaks of interest for the unknown phase, and used program TREOR
> to autoindex the unknown and identify the impurity phases. We then extracted
> intensities using the LeBail method, and determined the structure using direct
> methods with program SIRPOW. The structure was then refined with GSAS. We were
> even able to locate the H atom from Fourier maps!
>
> Even 20 years ago, it was possible to determine the structure from X-ray 
> powder
> patterns.
>
> Larry
>
>
>
++
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++

Re: Rietveld website cancelled ?

[Larry Finger]

On 08/29/2018 02:01 PM, Le Bail Armel wrote:

OK, seems that the SDPD book preface looks unclear to some.

Western movies adepts well know that sentence :

"You see, in this world there's /two kinds/ of /people/, my friend: /those/ with 
loaded /guns/, and /those/ who /dig/. /You dig/. .."


Similarly, there are two kinds of people, those believing that the sense of the 
words "structure determination" and


"structure refinement" are the same, and the others. You dig.


I am happy to have been one of the "others". I also know the difference between 
lattice and structure. :)


Larry

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Re: Rietveld website cancelled ?

[Le Bail Armel]

OK, seems that the SDPD book preface looks unclear to some.

 

Western movies adepts well know that sentence :

"You see, in this world there's two kinds of people, my friend: those with 
loaded guns, and those who dig. You dig. .."

 

Similarly, there are two kinds of people, those believing that the sense of the 
words "structure determination" and


"structure refinement" are the same, and the others. You dig.


 

Best


 

Armel


 

 

 

 

> Message du 29/08/18 18:09
> De : "Larry Finger" 
> A : "Le Bail Armel" , Rietveld_L@ill.fr
> Copie à : 
> Objet : Re: Rietveld website cancelled ?
> 
> On 08/29/2018 04:15 AM, Le Bail Armel wrote:
> > Hi,
> > 
> > After the IUCr Monograph on Crystallography 13 (2002)
> > 
> > entitled "Stucture Determination from Powder Diffraction Data"
> > 
> > you may find in the preface :
> > 
> > "Although the Rietveld method of structure refinement from powder
> > 
> > diffraction data is often loosely considered to be synonymous with structure
> > 
> > determination, it is not. The Rietveld method only comes into play in the
> > 
> > final stage of the structure solution process when an approximate structural
> > 
> > model has been found."
> > 
> > WIF David, K Shankland, LB McCusker, C Baerlocher
> > 
> > A clear distinction having my complete agreement.
> > 
> > Armel
> 
> Armel,
> 
> Although the above statement may be generally true, I can provide a counter 
> example. In Max W. Schmidt, Larry W. Finger, Ross J. Angel, and Robert E. 
> Dinnabier, "Synthesis, crystal structure, and phase relations of AlSiO2OH, a 
> high pressure hydrous phase", American Mineralogist, V. 83, 881-888, 1998, we 
> only had a powder - no single crystals. From data measured at ESRF, we used 
> GSAS 
> to isolate the peaks of interest for the unknown phase, and used program 
> TREOR 
> to autoindex the unknown and identify the impurity phases. We then extracted 
> intensities using the LeBail method, and determined the structure using 
> direct 
> methods with program SIRPOW. The structure was then refined with GSAS. We 
> were 
> even able to locate the H atom from Fourier maps!
> 
> Even 20 years ago, it was possible to determine the structure from X-ray 
> powder 
> patterns.
> 
> Larry
> 
> 
>++
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++

Re: Rietveld website cancelled ?

[Peter Y. Zavalij]

It all depends on the definition. If/when we agree on the definition, there
is usually no points for further arguing.
Anyway we could call Relieved method a structure determination from powder
data as long as it does not included solving structure (or as David
elegantly put - true structural solution).
Peter

Peter Y. Zavalij
Director - X-ray Crystallographic Center
University of Maryland,
College Park, MD 20742



On Wed, Aug 29, 2018 at 12:38 PM David Elbert  wrote:

> Absolutely important that people understand that the Rietveld method is
> structure refinement and not solution, but as Larry points out sometimes
> you can get a more out of it if you’re clever… and have no other choice!
> Here’s a second example:
>
> Stubbs et al., 2010, Uranyl phosphate sheet reconstruction during
> dehydration of metatorbernite [Cu(UO2)2(PO4)2·8H2O], American
> Mineralogist 95 (8-9): 1132-1140 which is a bit of a brute-force approach
> to implying structures of some uranyl phosphates in a synchrotron heating
> experiment.  Joanne Stubbs sorted through known structures of related
> materials and used observed trends in refinements to select similar
> structures to further investigate.  Able to then postulate reasonable
> structures which then refined to the observed data and provided insight
> into this interesting group of materials.
>
> Not the standard way to employment of Rietveld Refinement and certainly
> not true structural solutions, but a smart, useful, and rather satisfying
> application nonetheless.
>
> Best-
> David
>
> David Elbert
> Hopkins Extreme Materials Institute
> Malone Hall
> Johns Hopkins University
> 3400 N. Charles St
> Baltimore, MD 21218
>
> (410) 516-5049
>
> elb...@jhu.edu
>
>
>
>
>
>
>
>
> On Aug 29, 2018, at 12:09 PM, Larry Finger 
> wrote:
>
> On 08/29/2018 04:15 AM, Le Bail Armel wrote:
>
> Hi,
> After the IUCr Monograph on Crystallography 13 (2002)
> entitled "Stucture Determination from Powder Diffraction Data"
> you may find in the preface :
> "Although the Rietveld method of structure refinement from powder
> diffraction data is often loosely considered to be synonymous with
> structure
> determination, it is not. The Rietveld method only comes into play in the
> final stage of the structure solution process when an approximate
> structural
> model has been found."
> WIF David, K Shankland, LB McCusker, C Baerlocher
> A clear distinction having my complete agreement.
> Armel
>
>
> Armel,
>
> Although the above statement may be generally true, I can provide a
> counter example. In Max W. Schmidt, Larry W. Finger, Ross J. Angel, and
> Robert E. Dinnabier, "Synthesis, crystal structure, and phase relations of
> AlSiO2OH, a high pressure hydrous phase", American Mineralogist, V. 83,
> 881-888, 1998, we only had a powder - no single crystals. From data
> measured at ESRF, we used GSAS to isolate the peaks of interest for the
> unknown phase, and used program TREOR to autoindex the unknown and identify
> the impurity phases. We then extracted intensities using the LeBail method,
> and determined the structure using direct methods with program SIRPOW. The
> structure was then refined with GSAS. We were even able to locate the H
> atom from Fourier maps!
>
> Even 20 years ago, it was possible to determine the structure from X-ray
> powder patterns.
>
> Larry
>
>
> ++
> Please do NOT attach files to the whole list  >
> Send commands to  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  >
> Send commands to  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/
> ++
>
>
++
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Send commands to  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/
++

RE: Rietveld website cancelled ?

[Von Dreele, Robert B.]

Hi Armel,
A more extreme example was in Acta D56, 1549-1533 (2000) where a protein 
structure (a new insulin phase) was solved by rigid body Rietveld refinement 
from a synchrotron powder data set & subsequently confirmed by a single crystal 
analysis (see Acta Cryst. (2001). D57, 1091-1100). NB: this kind of thing has 
also happened more recently (see papers by Margiolaki, et al).
Bob Von Dreele

-Original Message-
From: rietveld_l-requ...@ill.fr  On Behalf Of Larry 
Finger
Sent: Wednesday, August 29, 2018 11:10 AM
To: Le Bail Armel ; Rietveld_L@ill.fr
Subject: Re: Rietveld website cancelled ?

On 08/29/2018 04:15 AM, Le Bail Armel wrote:
> Hi,
> 
> After the IUCr Monograph on Crystallography 13 (2002)
> 
> entitled "Stucture Determination from Powder Diffraction Data"
> 
> you may find in the preface :
> 
> "Although the Rietveld method of structure refinement from powder
> 
> diffraction data is often loosely considered to be synonymous with 
> structure
> 
> determination, it is not. The Rietveld method only comes into play in 
> the
> 
> final stage of the structure solution process when an approximate 
> structural
> 
> model has been found."
> 
> WIF David, K Shankland, LB McCusker, C Baerlocher
> 
> A clear distinction having my complete agreement.
> 
> Armel

Armel,

Although the above statement may be generally true, I can provide a counter 
example. In Max W. Schmidt, Larry W. Finger, Ross J. Angel, and Robert E. 
Dinnabier, "Synthesis, crystal structure, and phase relations of AlSiO2OH, a 
high pressure hydrous phase", American Mineralogist, V. 83, 881-888, 1998, we 
only had a powder - no single crystals. From data measured at ESRF, we used 
GSAS to isolate the peaks of interest for the unknown phase, and used program 
TREOR to autoindex the unknown and identify the impurity phases. We then 
extracted intensities using the LeBail method, and determined the structure 
using direct methods with program SIRPOW. The structure was then refined with 
GSAS. We were even able to locate the H atom from Fourier maps!

Even 20 years ago, it was possible to determine the structure from X-ray powder 
patterns.

Larry


++
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Send commands to  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/
++

Re: Rietveld website cancelled ?

[Larry Finger]

On 08/29/2018 04:15 AM, Le Bail Armel wrote:

Hi,

After the IUCr Monograph on Crystallography 13 (2002)

entitled "Stucture Determination from Powder Diffraction Data"

you may find in the preface :

"Although the Rietveld method of structure refinement from powder

diffraction data is often loosely considered to be synonymous with structure

determination, it is not. The Rietveld method only comes into play in the

final stage of the structure solution process when an approximate structural

model has been found."

WIF David, K Shankland, LB McCusker, C Baerlocher

A clear distinction having my complete agreement.

Armel


Armel,

Although the above statement may be generally true, I can provide a counter 
example. In Max W. Schmidt, Larry W. Finger, Ross J. Angel, and Robert E. 
Dinnabier, "Synthesis, crystal structure, and phase relations of AlSiO2OH, a 
high pressure hydrous phase", American Mineralogist, V. 83, 881-888, 1998, we 
only had a powder - no single crystals. From data measured at ESRF, we used GSAS 
to isolate the peaks of interest for the unknown phase, and used program TREOR 
to autoindex the unknown and identify the impurity phases. We then extracted 
intensities using the LeBail method, and determined the structure using direct 
methods with program SIRPOW. The structure was then refined with GSAS. We were 
even able to locate the H atom from Fourier maps!


Even 20 years ago, it was possible to determine the structure from X-ray powder 
patterns.


Larry


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Re: Rietveld website cancelled ?

[Le Bail Armel]

 

>Very few citations though;

 

The fact is that you don't cite this couple of examples in your own list of 
selected publications :

http://hewat.net/science/

If you find them of poor interest, the World follows you.

 

Armel

 

PS - A positive search-match (using the COD) signifies that the structure is 
already determined (not always if you use ICDD), then if you wish, you may 
refine it by the Rietveld method

 

 

> Message du 29/08/18 12:35
> De : "Alan Hewat" 
> A : "Armel Le Bail" 
> Copie à : "rietveld_l@ill.fr" 
> Objet : Re: Rietveld website cancelled ?
> 
>
> A clear distinction having my complete agreement. (Armel)
Ouf. Nous sommes d'accord enfin :-) For Armel, here are a couple of examples of 
automatic indexing, search-match and structure DETERMINATION from neutron 
powder data. Very few citations though; crystallographers largely ignored 
neutron powder diffraction before 1987 and Hi-Tc :-)


__
>
   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE 
+33.476.98.41.68
>         http://www.NeutronOptics.com/hewat
> __






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Re: Rietveld website cancelled ?

[Alan Hewat]

> A clear distinction having my complete agreement. (Armel)
Ouf. Nous sommes d'accord enfin :-) For Armel, here are a couple of examples

of automatic indexing, search-match and structure DETERMINATION from
neutron powder data. Very few citations though; crystallographers largely
ignored neutron powder diffraction before 1987 and Hi-Tc :-)
__
*   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE *
 +33.476.98.41.68
http://www.NeutronOptics.com/hewat
__
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RE: Rietveld website cancelled ?

[Le Bail Armel]

Hi,

 

After the IUCr Monograph on Crystallography 13 (2002)

entitled "Stucture Determination from Powder Diffraction Data"

you may find in the preface :

"Although the Rietveld method of structure refinement from powder

diffraction data is often loosely considered to be synonymous with structure

determination, it is not. The Rietveld method only comes into play in the

final stage of the structure solution process when an approximate structural

model has been found."

WIF David, K Shankland, LB McCusker, C Baerlocher

 

A clear distinction having my complete agreement.

 

Armel

http://www.cristal.org/CAC-XX/maze.jpg

http://www.cristal.org/CAC-XX/Rietveld.ppt

 

 

> Message du 29/08/18 10:14
> De : "May, Frank" 
> A : "Alan Hewat" , "rietveld_l@ill.fr" 
> Copie à : 
> Objet : RE: Rietveld website cancelled ?
> 
> To all:
> 
> Initially I sent this to Alan who suggested I open discussion to the entire 
> community. I've posted similar in past years and have been FLAMED. Please 
> keep it civil. ;-)
> =
> As a long time practitioner of powder XRD (since 1972) I was there when the 
> superconductor craze hit in the mid-1980s. At that time it was recognized the 
> Rietveld Method was useful only for REFINING structures which were generally 
> accepted from single crystal x-ray analysis.
> 
> The http://www.cristal.org/rietv025/ link says the method "[allows] an 
> accurate determination of the structure." I take that statement to mean no 
> model is required; Rietveld Analysis can determine structure without 
> preconceived model.
> 
> Thanks for reading.
> 
> Blessings from toasty and warm St. Louis, MO.
> 
> Frank May
> Research Investigator
> University of Missouri-St. Louis
> 
> formerly at Monsanto Company (which recently became part of 
> BAYER)++
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RE: Rietveld website cancelled ?

[May, Frank]

To all:

Initially I sent this to Alan who suggested I open discussion to the entire 
community.  I've posted similar in past years and have been FLAMED.  Please 
keep it civil.  ;-)
=
As a long time practitioner of powder XRD (since 1972) I was there when the 
superconductor craze hit in the mid-1980s.  At that time it was recognized the 
Rietveld Method was useful only for REFINING structures which were generally 
accepted from single crystal x-ray analysis.

The http://www.cristal.org/rietv025/ link says the method "[allows] an accurate 
determination of the structure."  I take that statement to mean no model is 
required; Rietveld Analysis can determine structure without preconceived model.

Thanks for reading.

Blessings from toasty and warm St. Louis, MO.

Frank May
Research Investigator
University of Missouri-St. Louis

formerly at Monsanto Company (which recently became part of BAYER)++
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Re: Rietveld website cancelled ?

[Alan Hewat]

Good work Armel. Note that little is lost once it is posted to the WWW,
since it is backed up in several places. The "WayBack Machine" is a good
way of recovering historic web sites. The WayBack server is a bit slow,
since it is supported only by donations and is probably in heavy demand -
see:
https://web.archive.org/web/20180212154506/http://home.wxs.nl/~rietv025/

On Tue, 28 Aug 2018 at 17:15, Le Bail Armel  wrote:

>
>
> http://home.wxs.nl/~rietv025/
>
> It has suddenly disappeared a few days ago.
>
>
>
> A copy can be found here :
>
> http://www.cristal.org/rietv025/
>
>
>
> Armel
>
>
>
>
>
>
>
>
> ++
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> text
> The Rietveld_L list archive is on
> http://www.mail-archive.com/rietveld_l@ill.fr/
> ++
>
>

-- 
__
*   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE *
 +33.476.98.41.68
http://www.NeutronOptics.com/hewat
__
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