Re: [sdpd] Giant and still so big

[Franck Millange <millange...@chimie.uvsq.fr>]

Dear Armel,

First of all, Thank you for your comments about the compound labelled MIL-100.

Armel wrote : "However, if I was asked to explain how the structure was 
solved exactly, I would be unable...
- pure prediction ? then matching with the powder pattern ?
- or "prediction" knowing the cell parameters (which would be in fact 
"structure determination") and moving moieties inside of the cell by global 
optimization ? Would be interesting to know exactly."

You will be able to find more details in the papers published in Angew Chem 
(2004, vol 43, page 6285-6301).


Armel wrote : "And these limits were estimated for FWHM close to 0.02° 
(2-theta). So, for 0.01° FWHM, you would have to multiply by 2...
Not far beyond - just inside the range. At ACA'97, such 0.01° FWHM was 
already available and the estimation given was 576.000A**3 for a F-centered 
cubic cell."

I am afraid to say that this compound is beyond and NOT inside the range 
because we've got a ~0.023° FWHM (first (111) hkl reflection, d= 42.1 Å) 
for this compound using the ID-31 beamline so a V = 387000 A**3 is still 
higher than the estimation limit of V=288000 A**3 for FWHM close to 0.02°. 
Anyway, soon another results will be published with same FWHM BUT with a 
V=706.000 A**3 (Fd-3m S.G.)...

Regards

Franck


A 13:49 24/02/2005 +0100, Armel Le Bail a écrit :

>Hi,
>
>I would like to congratulate the authors of the
>SDPD of a giant cubic structure (SG; Fd-3m;
>a = 72.26 A, V = 387000 A**3) named MIL-100 :
>http://www3.interscience.wiley.com/cgi-bin/abstract/109803129/ABSTRACT
>http://www3.interscience.wiley.com/cgi-bin/abstract/109605226/ABSTRACT
>See also the ESRF Highlights 2004, p. 25-26.
>
>However, if I was asked to explain how the
>structure was solved exactly, I would be unable...
>- pure prediction ? then matching with the powder pattern ?
>- or "prediction" knowing the cell parameters (which
>     would be in fact "structure determination") and moving
>     moieties inside of the cell by global optimization ?
>
>Would be interesting to know exactly.
>
>Armel
>
>PS - It is said that 387.000 A**3 is "far beyond the
>current possibilities for solving the structure from
>ab initio procedures."
>
>Well, it was written in the SDPD tutorial in 1992 that
>"Triclinic centrosymmetrical cells with up to 3000 Å3
>volume or cubic cells with F lattice as large as 300.000 Å3
>are the theoretical upper limits which one could expect to
>attain by using high resolution synchrotron data !
>http://www.cristal.org/iniref/tutorial/part3a.html#3.1
>
>And these limits were estimated for FWHM close to 0.02°
>(2-theta). So, for 0.01° FWHM, you would have to multiply by 2...
>
>Not far beyond - just inside the range.
>
>At ACA'97, such 0.01° FWHM was already available
>and the estimation given was 576.000A**3 for a F-centered
>cubic cell. See the slide :
>http://www.cristal.org/iniref/aca97/t18.gif
>http://www.cristal.org/iniref/aca97/aca97.html
>
>So the race to the largest structure solved by SDPD is
>continuing... But at least, please explain how exactly
>you solved your structure...
>
>
>
>
>
>Yahoo! Groups Links
>
>
>
>


[Non-text portions of this message have been removed]



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