Re: [sdpd] structure and structureless lattice determination

[Jacco van de Streek <streek...@ccdc.cam.ac.uk>]

Armel Le Bail wrote:
> 
> >Do you have a reference? As I never refine the cell parameters obtained by the
> >Pawley fit, this is not purely an academic point for me.
> 
> Well, I can show perfect whole profile fitting without structure
> constraint by using incorrect cells.

The original poster referred to a situation where the correct unit cell is
known, but the exact values of the lattice parameters as obtained by
Pawley/LeBail vs. Rietveld fits were (I assumed, slightly, but no longer within
experimental error) different.

> If you always stop at that step
> without any Rietveld fit probably you study only already known
> compounds.

Obviously, the crystal structure itself should be refined by Rietveld refinement
to establish the *correctness* of the unit cell (and crystal structure). But I
cannot see any arguments why the *values* of cell parameters taken from a Pawley
fit should ever be refinement during Rietveld refinement (and moreover, I can
see arguments why they shouldn't be).

Best wishes,
-- 
Jacco van de Streek
Research Scientist
Cambridge Crystallographic Data Centre
Cambridge, United Kingdom

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