Hi Prasun, I would be very cautious about placing too much value upon the statistics, when the quality of the fit to the actual observed data is far more important - do the refined and observed peaks match, are there extra reflections, how do the peak shapes actually look etc. It is possible to get a very good statistical fit to data and still have fitted using the wrong space group and so on.
Ideally speaking of course, the 'best' Chi^2 is 1.0, in practice anything below 5 indicates that you are getting towards a good statistical fit - but check the plots! See also these excellent papers: R factors in Rietveld analysis: How good is good enough? By Brian Toby in POWDER DIFFRACTION Volume: 21 Issue: 1 Pages: 67-70 and Rietveld refinement of a wrong crystal structure By Christian Buchsbaum and Martin U. Schmidt in ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE Volume: 63 Pages: 926-932 Part: Part 6 Hope this helps, Dr Nik Reeves XRD Lab Manager, Department of Engineering Materials, University of Sheffield -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: 19 August 2008 09:30 To: Rietveld Method Subject: GSAS: Good fit Can anyone tell me upto what value of chi^2 an XRD whole profile fit will be called as a good fit in GSAS?? I am getting a chi^2 value around 2.1 to 2.3, are those good fits? thanking in advance, Prasun
