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

[Armel Le Bail <armel...@fluo.univ-lemans.fr>]

>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/