Truecell searches for more symmetric, higher symmetry cells that could be a "better" solution to powder indexing data. This can be useful where powder indexing programs favour small, low symmetry cells; and a higher volume, higher symmetry cell could be a better solution. Truecell can read *.SUM Summary results files generated by the Crysfire Powder Indexing Suite by Robin Shirley
CHEKCELL: Graphical Powder Indexing helper and Spacegroup Assignment Software now has a version of Truecell included with it (accessible via the "Cell Parameters" window). Refer to the Chekcell tutorials for information involving Chekcell.
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Truecell (and Chekcell) can be obtained off the web at the the LMGP
(Laboratoire des Materiaux et du Génie Physique de l'Ecole Supérieure de
Physique de Grenoble http://www.inpg.fr/LMGP/)
program suite site at:
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The example data file is of a cubic Y2O3 sample using Indexing results from the
Crysfire Powder Indexing Suite
by Robin Shirley. Crysfire can be run concurrently with Truecell and Chekcell but this assumes you already have some trial cells from Crysfire in the Crysfire *.SUM summary file. To see tutorials and obtain Chekcell, refer to the LMGP Suite Main Page. In this demonstration, we will look at the best FOM result and find out what higher symmetry cells Truecell can generate, then match to other solutions. |
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Click on the Truecell icon or run the program via the windows explorer/windows file manager to
bring up the Truecell starting interface.
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Select the Crysfire icon to be prompted to open up a Crysfire *.SUM file and
select the file of interest. In this case, Crysfire has logged over 4000 trial cells.
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Click on the desired cell that you wish to perform a Truecell analysis on; tweak any
parameters though the defaults are decently robust; then press the Run icon to
start Truecell looking for alternative cells. A "% complete" bar will give an
indication on how long this will take. In this case, we will choose the top FOM monoclinic
cell.
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Truecell will then present any resulting cells it has found, the transformation
matrix and whether it matches up with any other found solutions.
In this case Truecell has found a number of cells, including an hexagonal/rhombohedral cell which matches up with solution 166; (which also happens to be the true cell for this phase as found by TEM). Performing a "Best Solution" analysis in the Chekcell software (which is part of the LMGP Suite) would flag this hexagonal cell with a spacegroup of R3, R-3, R32, R3M and R-3M as the best suggested solution. As Truecell is also incorporated inside Chekcell, all of this could have course been conveniently performed inside chekcell.
Of course this is quite a contrived example as the "real" answer is known. In the case of an unknown, it is up to the user to choose the "best" and hopefully "true" cell. Truecell (and Chekcell) can give some extra and possibly vital food for thought. |
