Dear
Colleagues,
Since the
SDPD group apparently disappeared from Yahoo, I’m answering a query raised there
some time ago using this yet unrestrained list. The query record is attached
after the message.
The crystal
structure solution of decafluorocyclohexene announced in the SDPD list as “a 32
years story involving Pawley and Le Bail methods + DFT” is found to be
incomplete. Now the structure is completed by an additional alternative
molecular orientation and successfully refined using original neutron powder
data:
http://dx.doi.org/10.1107/S2052520613031028
So, DFT is
a powerful and useful tool, indeed, but real reliable structure solution still
requires careful analysis of experimental data.
DFT is DFT,
but it doesn’t guarantee. ;-)
Best
regards,
Leonid
*******************************************************
Leonid A. Solovyov
Institute of Chemistry and Chemical Technology
660036, Akademgorodok 50/24, Krasnoyarsk, Russia
http://sites.google.com/site/solovyovleonid
*******************************************************
“a 32 years story involving Pawley and Le Bail methods + DFT” history:
Hi,
C6F10 was
chosen long ago as the test case for demonstrating the
abilities
of a new method suggested by Pawley (1981) for accurate
extraction
of peak positions and intensities from powder diffraction
scans.
http://dx.doi.org/10.1107/S0021889881009618
Funny
enough, the structure awaited 2013 to be determined by a
combination
of Le Bail method, direct space structure solution and
DFT, using
the Pawley original neutron data :
http://dx.doi.org/10.1107/S2052519213013365
No doubt
that improvement is still possible.
Best
wishes,
Armel
>Funny
enough, the structure awaited 2013 to be determined by a
>combination
of Le Bail method, direct space structure solution and
>DFT,
using the Pawley original neutron data:
>http://dx.doi.org/10.1107/S2052519213013365
Rather
eccentric choice of data in the form of a simulated pattern. It seems that in
the future structures will be solved without experiment.
A
comparison of the real powder pattern with a calculated one based on the solved
structure model gives a horrible fit:
http://sites.google.com/site/ddmsuite/home/C6F10-LeBail-DFT.png
Something
is apparently wrong in the proposed structure model (or in the data).
*******************************************************
Leonid A.
Solovyov
Instituteof Chemistryand Chemical Technology
660049, K.
Marx 42, Krasnoyarsk, Russia
http://sites.google.com/site/solovyovleonid
*******************************************************
>Something
is apparently wrong in the proposed
>structure
model (or in the data).
Yes. Some
ice maybe ? I don't know. It was not sure that the 2-theta max was
really ~54°
(wavelength ~1.9 A, neutron, D1A), a
long search
for the original data
failed, so
that the Pawley extracted intensities were used.
But I
wanted to give you another chance to apply
your vision
of structures refined
without
restraints. In that case, 64 x,y,z
coordinates
and ~90 largely overlapping
peaks. Is
that your limit ? No model improvement that time ? I must say that it
was even my
limit for refinement with soft
restraints
;-), hence the DFT approach,
but the
solution stage could even be realized routinely by DASH (etc).
Possibly
someone there in the world is currently making again the experiment
in order to
obtain better data... Wait & see. We already waited 32 years...
Best,
Armel
>long
search for the original data
>failed,
so that the Pawley extracted intensities were used.
The
original pattern is readily available in the data-file of the Pawley's program
ALLHKL:
http://www.ccp14.ac.uk/solution/pawley/allhkl/inifile.txt
>But I
wanted to give you another chance to apply
>your
vision of structures refined
Before the
refinement one needs to find a valid structure model. So, in the future,
probably...
*******************************************************
Leonid A.
Solovyov
Instituteof Chemistryand Chemical Technology
660049, K.
Marx 42, Krasnoyarsk, Russia
http://sites.google.com/site/solovyovleonid
*******************************************************
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