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Re: [sdpd] For Powder Indexing: New Truecell software and Truecell enabled Chekcell update
Thank you for the answer.
I have not tried the the Crysfire Suite on this problem yet. I thought
there might be a simpler way of deriving a smaller cell from an oversized
supercell.
I am not completely sure what you mean when you say "Are there trace peaks
that could be removed to see what resulting cells occur?" What are the
"trace peaks" you are referring to?... Do you mean weak peaks, with a low
precision on their position?
Thank you for the suggestions. I will try them.
Cheers,
Georges
=========================================================================
At 08:21 PM 5/26/00 +0100, you wrote:
>
>> I have the reverse problem: one superstructure reflection forces me to
>> quadrupole the three parameters, i.e. a, b and c of an orthorhombic basic
>> cell, which multiplies the volume by 64. However, I suspect there might be
>> a smaller unit-cell, with a different orientation of the unit-cell axes,
>> and possibly a different crystal system. I am wondering how to check this
>> and find possible smaller cells that would index every peak. In addition
>> to the superstructure reflection, there are many new peaks, weaker,
>> however, they are at higher angles where there are too many choices of
>> indexation in the 4a x 4bx 4c supercell. Anybody has an idea how to tackle
>> this problem?
>> Every suggestion will be welcome.
>> Thank you.
>>
>> Georges
>>
>
>In the case of the Crysfire Suite - have you tried using all 7
>applicable indexing programs on this data (ito, treor, dicvol,
>taup, lzon, fjzn and kohl)?
> http://www.ccp14.ac.uk/tutorial/crys/
>(Plugging the resulting Crysfire Summary file into Chekcell
>would allow you to quickly evaluate the various solutions which
>could be many and varied)
>
>Each indexing program has its various strengths and one can
>succeed where all others fail. Are there trace peaks that
>could be removed to see what resulting cells occur? The
>low precision of the trace impurity peak positions could also
>be throwing things out.
>
>-----
>
>Another option is to use fundamental parameters fitting of
>the peaks to allow for the geometry abberations of Bragg
>Brentano XRDs that cause peak position changes. As said on
>previous occassions, using Fundamental Parameters can
>gives peak results from Bragg Brentano XRDs, as though the
>data was collected on an "ideal" XRD.
>
>XFIT peak profiling software for Win95/Win98 can do the job here:
>(but you have to know the slit and geometry settings of
>the XRD equipment your data was collected with)
>Example FP examples at:
>
> http://www.ccp14.ac.uk/tutorial/xfit-95/fun1.htm
> http://www.ccp14.ac.uk/tutorial/xfit-95/liti/rwfunpar.htm
>
>
>I have not got a tutorial on-line comparing the two main peak profiling
>methods for indexing - but using fundamental parmeters peak profiling
>can make quite a positive difference to the Figure Of Merits and
>suggested cells produced by the indexing programs.
>
>Lachlan.
>
>> =====================================================================
>>
>> At 06:10 AM 5/26/00 +0100, you wrote:
>> >
>> >There is are new addition to the LMGP suite by Jean Laugier and
>> >Bernard Bochu called "Truecell".
>> >
>> >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.
>> >
>> >The Chekcell graphical powder indexing helper and spacegroup
>> >assignment software now has a version of Truecell included with it -
>> >accessible via the "Cell Parameters" window.
>> >
>> >(Truecell (and Chekcell) can read *.SUM Summary results files generated
>> >by the Crysfire Powder Indexing Suite by Robin Shirley)
>> >
>> >Tutorial runthroughs showing Truecell in action are available
>> >from the CCP14 website:
>> >
>> > Basic Demonstration of Truecell on Y2O3 Crysfire results
>> > http://www.ccp14.ac.uk/tutorial/lmgp/trucella.htm
>> >
>> > Using Truecell on a high FOM monoclinic trial solution
>> > http://www.ccp14.ac.uk/tutorial/lmgp/truecell_large_hex.htm
>> >
>> >----
>> >
>> >Truecell and Chekcell Download:
>> > UK: http://www.ccp14.ac.uk/ccp/web-mirrors/lmgp-laugier-bochu/
>> > CA: http://ccp14.sims.nrc.ca/ccp/web-mirrors/lmgp-laugier-bochu/
>> > AU:
>>
ftp://ftp.minerals.csiro.au/pub/xtallography/ccp14/ccp/web-mirrors/lmgp-laug
>> ier-bochu/
>> >
>> >
>> >Crysfire Powder Indexing Suite Download:
>> > UK: http://www.ccp14.ac.uk/ccp/web-mirrors/crys-r-shirley/
>> > CA: http://ccp14.sims.nrc.ca/ccp/web-mirrors/crys-r-shirley/
>> > AU:
>>
ftp://ftp.minerals.csiro.au/pub/xtallography/ccp14/ccp/web-mirrors/crys-r-sh
>> irley/
>> >
>
>
>--
>Lachlan M. D. Cranswick
>
>Collaborative Computational Project No 14 (CCP14)
> for Single Crystal and Powder Diffraction
>Daresbury Laboratory, Warrington, WA4 4AD U.K
>Tel: +44-1925-603703 Fax: +44-1925-603124
>E-mail: l.cranswick...@dl.ac.uk Ext: 3703 Room C14
> http://www.ccp14.ac.uk
>
>