Re: [sdpd] For Powder Indexing: New Truecell software and Truecell enabled Chekcell update

[Georges Denes <gdenes...@vax2.concordia.ca>]

Thank you, Armel for your excellent suggestion.

Georges

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At 04:35 PM 5/27/00 +0200, 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. 
>
>Using words such as "superstructure reflection" would mean that the
>substructure was determined, but you did not say if the substructure was
>determined. In fact, there are two possibilities for tackling this problem 
>(supposing that there is no modulation or misfit and so on) :
>
>- First determine the structure in the subcell. This will allow you
>to consider that the unindexed reflections are either impurities
>or really superstructure reflections. In the second case, DICVOL
>being exhaustive is the best program for trying to obtain new
>cells by adding the superstructure ones. Anyway, if you do have 
>only one clear superstructure reflection, I think that you will never
>be able to refine the 4x4x4 superstructure, and nobody will complain
>if you give only the coordinates in the subcell.
>
>- If you cannot determine the structure in the subcell, you may
>consider that your super and substructure hypothesis was not correct,
>and try again to index, or make new syntheses varying the chemical
>composition in order to detect multiple phases.
>
>Best wishes,
>
>
>Armel Le Bail - Université du Maine, Laboratoire des Fluorures,
>CNRS ESA 6010, Av. O. Messiaen, 72085 Le Mans Cedex 9, France
>http://www.cristal.org/
>