Re: [sdpd] Synchrotron powder diffraction

[Armel Le Bail <alb...@cristal.org>]

>   => Conventional Rietveld Rp,Rwp,Re and Chi2:  12.3 16.4 7.28 5.050

OK, the main change is on the Rexpected which has now twice the
value I reported by using wrong esds  :

=> Conventional Rietveld R-factors for Pattern: 1 
=> Rp: 14.0 Rwp: 16.5 Rexp: 3.99 Chi2: 17.1 

and since the reduced chi-squared goodness-of-fit is the
Rwp/Rexp ratio, the change is dramatic on Chi2.

I must confess that I have never trusted a lot anything based
on Rexpected, but this is an old Rietveld dabate, not a SDPD
debate. The fact is that multiplying your data by any factor
immediately changes Rexpected. You can always get Chi2=1 
with conventional X-ray data by choosing a proper rescaling factor
or by counting less or by counting more time (of course I don't do 
that ;-). I prefer to trust first Rp and I never give a look at Chi2.

Armel
http://www.cristal.org/course/


------------------------ Yahoo! Groups Sponsor ---------------------~-->
Get your FREE credit report with a FREE CreditCheck
Monitoring Service trial
http://us.click.yahoo.com/MDsVHB/bQ8CAA/ySSFAA/UIYolB/TM
---------------------------------------------------------------------~->

 

Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/