recall and introduction to
cell constraint WPPF for "|Fobs|" extraction
The concept is a kind of response
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 :