Now I am trying to understand the fundamental difference between full pattern PDF refinement and full pattern Rietveld refinement. For example, in http://prola.aps.org/abstract/PRB/v60/i14/p9973_1 Th.Proffen et al. have a nice report on using both types of refinement (GSAS and PDFFIT) on the same data for LaMnO3. (The PDF and Rietveld refinements agree :-) They say about PDFFIT:
This is is exactly analogous to the Rietveld method except that the PDF is fit in real space rather than the reciprocal-space data...
Thermal factors obtained from PDF refinements are often more accurate than Rietveld thermal factors because of the wider range of Q over which data are analyzed. For example, in this study the PDF�s were obtained from data collected up to Qmax=27�-1 This is almost double the Q range used (Qmax=15.7�-1) in the Rietveld refinement of the same data. The Rietveld refinement was confined to a lower Q range due to Bragg-peak overlap in the high-Q region.
So my questions are naturally:
1) Could not the Rietveld refinement also be extended to the full data range ?
2) If that was done, would there be any fundamental difference between the two methods of fitting ?
(Yes, I know they also refined on a restricted d-spacing interval containing only Mn-O distances, and that there are other advantages to PDF analysis in identifying features that may not be included in the model).
But if you refine the full data with the same model, can there really be any fundamental difference, if in one case you simply do a Fourier transform to real space ? What am I missing here ?
Alan.
Alan Hewat, ILL Grenoble, FRANCE <[EMAIL PROTECTED]> fax (33) 4.76.20.76.48
(33) 4.76.20.72.13 (.26 Mme Guillermet) http://www.ill.fr/dif/AlanHewat.htm
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