Re: [sdpd] Reduced Cell?

[Armel Le Bail <alb...@cristal.org>]

>Could you please explain me how the reduce process works? 
>OR, Could you tell where can I find materials to study?

We are >260 subscribers now to the SDPD mailing list which
could answer. But if you want a response especially from me, 
here it is :

The Bible on that question is "International Tables for Crystallography",
Volume A, Chapter 9 (Crystal Lattices) by H. Burzlaff, H. Zimmermann
and P.M. de Wolff (pages 734-744).

All lattices have alternative ways of describing the same periodicity.
Lattices provided by automatic indexing have to be examined, and
this is best done by reducing the lattice to a primitive cell following
conventions. There is a program (REDUCT) inside TREOR doing that.
The NBS*AIDS83 program is recommended for checking powder
diffraction data submitted to ICDD. There is a huge list of programs
performing metric analysis in the "World Directory of Powder
Diffraction Programs" by S. Gorter and D.K. Smith.

The example you give is a typical pitfall in monoclinic symmetry.
Alternative cells are graphically shown in the description of the 
space groups in the International Tables for Crystallography, Volume
A. They are obtained, in the unique axis b setting, by considering
the ac plane, building a new cell by keeping either a or c as cell
parameter and using the vector a+c for obtaining a new cell parameter.
The cell volume does not change.

Best,

Armel Le Bail
http://www.cristal.org/course/