Prsentation PowerPoint

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Getting Cell Parameters from Powder Diffraction
Data Armel Le Bail Université du Maine,
Laboratoire des Oxydes et Fluorures, CNRS UMR
6010, Avenue O. Messiaen, 72085 Le Mans,
FranceEmail alb_at_cristal.org
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Outline The Indexing Problem(s) Indexing
Software Indexing Benchmarks Demonstrations
(screen shots) Live Demonstrations
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The Indexing Problem(s)
1 to 6 unknownsmaximum a, b, c, ?, ?, ?
Data 20 first peak positions
Problem overdetermined,looks simple
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Difficulties come from - inaccuracy in peak
positions (due to zeropoint error, sample
misplacement, low resolution, bad crystallinity),
- the presence of impurities providing spurious
additional peaks, - the possibility to miss some
large high-symmetry cells which can also be
described in smaller sub-cells of lower symmetry,
- the fact that one of the a, b, c parameters
can be very short if compared to the two others
(dominant zone) so that the first diffraction
peak involving it through the hkl Miller indices
may not be included among the first 20 which will
be exclusively h0l lines for instance (if b is
small), - etc.
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INDEXING SOFTWARE The best description is in this
2003 Robin Shirley paper
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From Robin Shirley
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From Robin Shirley
Underlined are inside the CRYSFIRE package
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The Indexing Benchmarks
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(No Transcript)
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(No Transcript)
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Bergmann, J., Le Bail, A., Shirley, R.
Zlokazov, V. Zeitschrift für Kristallographie 219
(2004) 783-790.
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Demonstrations - Screenshots
WinPLOTR, PowderX(peak position hunting, and
more) McMaille, TREOR, DICVOL(indexing) CHEKCEL
L(visualization, and more) FULLPROF(cell-constr
ained whole pattern fitting, and more)
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ACADEMIC SOFTWARE WITH TRADITIONAL OPEN ACCESS
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WinPLOTR saving the Y2O3 peak positions for an
indexing program
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Typical data for indexing in automated mode with
McMaille  Y2O3! Wavelength, zeropoint and NGRID
(NGRID3 black box mode) 1.54056 0.000 3!
List of 2theta positions, intensity (min.20)
20.504 1411. 29.157 11198.
33.791 2632. 35.910 531.
37.921 135. 39.848 606.
41.700 118. 43.488 881.
46.889 271. 48.528 4213.
50.120 230. 51.685 66.
53.207 506. 54.697 117.
56.169 404. 57.614 2603.
59.035 563. 60.433 471.
61.811 194. 63.178 149.
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McMaille displaying its best results for Y2O3
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McM20 100./(RPN20) Br Sy,  N20 is the
number of possibly existing lines up to the
20th observed line (for a primitive P lattice).
Br is a factor arbitrarily set to 6 for F and R
Bravais lattices, 4 for I, 2 for A, B, C and 1
for P. Sy is a factor equal to 6 for a cubic or
a rhombohedral cell, 4 for a trigonal/hexagonal/te
tragonal cell, 2 for an orthorhombic cell, and 1
for a monoclinic or triclinic cell.
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WinPLOTR displaying the McMaille best cell for
Y2O3
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Background estimation with PowderX for ?-AlF3
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K?2 stripping with PowderX for ?-AlF3
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Peak positions hunting with PowderX for ?-AlF3
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McMaille displaying its best results for ?-AlF3
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F.o.M. for ?-AlF3
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Examining with Chekcell the list of most probable
?-AlF3 cells from McMaille
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Pawley or Le Bail methods are used for a
penultimate proof of the cell quality (the
ultimate being the structure solution and
refinement)
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The Le Bail fit of the ?-AlF3 conventional
laboratory powder pattern by using FULLPROF and
the P4/mmm space group, showing the possible
(hk0, hk 2n) extinction rule
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WinPLOTR saving the C28H24O8 data for TREOR
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TREOR running inside of WinPLOTR for C28H24O8
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The Le Bail fit of the C28H24O8 synchrotron
powder pattern by using FULLPROF selecting the
P21/c space group
Another plague of SDPD anisotropic line
broadening
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WinPLOTR saving the tetracycline hydrochloride
data for DICVOL
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Selection of the indexing conditions for DICVOL04
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DICVOL04 cell Proposition for the tetracycline
hydrochloride
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Live Demonstrations Once a (good) powder pattern
is recorded,and if the compound(s) remain
unidentified, the time needed for a successful
indexing is somewhere between 15 minutes and
never