Short recall and introduction to
cell constraint WPPF for "|Fobs|" extraction
 
 
 

The concept is a kind of response
to complexity
in powder diffractometry
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Not really needed with :

 
 

Absolutely necessary with :
(though some people think not)

So, we don't speak here of individual peak fit
 
 

Some dates for WPPF :
 
 

No cell constraint :
Taupin (1973) ; Sonneveld & Visser (1975).
Reflection profiles are fitted where you believe they are.
 

Cell constraint :
Pawley (1981) : least-squares fitting of the pattern.
Le Bail (1988) : iterations of the Rietveld decomposition formula.
Intensities are extracted where the reflections should be.
 

First applications of cell constraint WPPF to SDPD :
1987 (Pawley method) ; 1988 (Le Bail method).
 
 
 
 

Nowadays, for ~300 ab initio structure determination by powder diffractometry :