>I am doing powder refinement on a series of monoclinic samples. My main
>interest is the unit cell dimension change over the solid solution series,
>so I can't help wondering how is the quality & reliability of cell
>dimension results obtained via Le Bail method compared with Rietveld
>refinement. Lots of time can be saved if Rietveld refinement is not that
>necessary.
The title of the original G. S. Pawley paper is :
Unit-Cell Refinement from Powder Diffraction Scans
J. Appl. Cryst. 14 (1981) 357-361.
The Le Bail method does a similar job quite faster with a better
stability. Nevertheless I will not write that the quality and reliability of
cell dimension results obtained via Pawley or Le Bail methods are better
than those from Rietveld refinement. The quality may be either
- of the same order
- or really lower because the cell may be false (only the
successful structure refinement confirm a cell
proposition)
Conclusion : prefer the Rietveld method, the Moore law has reduced time
to 1/10000 for in-lab computers since 1981 ! Refining the rutile
structure on a PDP 11-23 needed 1 week by the Rietveld method
and 1 minute now...
Some additional words : the Pawley method was not used in order
to extract intensities for a real ab initio structure determination
before 1987. The slack constraints used for avoiding problems
in refining separately the intensities of two (or more) strictly
overlapping reflections lead to equipartitioning. Yes Bill,
equipartitioning applies to the data, not to the model. Without
data, no model is confirmed - and you use the Pawley method,
Bill, producing biased data as well as the Le Bail method. This
bias does not exist with the Rietveld method... What is your
secret, Bill, for having "the same thing" at the end ?
Armel