Dear Sanjay Sharma ,
The complete answer to your question takes several considerations.
Nevertheless, there is no simple way to distinguish a reasonable good fit from one that is just a set of wrong based on R factors or other discrepancies.
A large number of Rietveld indices (R-factors) have been proposed, there is no way, virtually impossible to pick up one that can be used as an absolute measure of refinement quality.
The reasons need to be clear; a good fit, not always means a low Bragg-R factor. It means a physically correct and acceptable description of the material. There are several ways to get relatively low Bragg-R factors completely meaningless; it is a widespread mistake.
Diffraction data are a set of intensities measured at a set of specific momentum transfer (Q) values, usually expressed as 2θ scanning.
Check the limitations and have a wild vision of the problem, so please read the reference below.
It is an excellent discussion on how good a fit is good enough.
https://www.cambridge.org/core/journals/powder-diffraction/article/r-factors-in-rietveld-analysis-how-good-is-good-enough/17439A1F889B689C495549A234D53682/core-reader
Best regards,
WNM
Dear Sanjay Sharma ,
The complete answer to your question takes several considerations.
Nevertheless, there is no simple way to distinguish a reasonable good fit from one that is just a set of wrong based on R factors or other discrepancies.
A large number of Rietveld indices (R-factors) have been proposed, there is no way, virtually impossible to pick up one that can be used as an absolute measure of refinement quality.
The reasons need to be clear; a good fit, not always means a low Bragg-R factor. It means a physically correct and acceptable description of the material. There are several ways to get relatively low Bragg-R factors completely meaningless; it is a widespread mistake.
Diffraction data are a set of intensities measured at a set of specific momentum transfer (Q) values, usually expressed as 2θ scanning.
Check the limitations and have a wild vision of the problem, so please read the reference below.
It is an excellent discussion on how good a fit is good enough.
https://www.cambridge.org/core/journals/powder-diffraction/article/r-factors-in-rietveld-analysis-how-good-is-good-enough/17439A1F889B689C495549A234D53682/core-reader
Best regards,
WNM
Dear, Sanjay wagner alraedy have explained very nicely, in brief I would say any value Rwp less than 5 is better to consider better Reitveld Refinement Fitting.
Dear Sanya, just looking at R-values during a Rietveld fit can be greatly deceiving. As previously mentioned lots of "Quality of fit" related indicators are produced during a fit, but finally, the refined model must be realistic. Also, the number of refined variables must be small (much smaller than the number of data, etc), with enough variables you can fit any dataset to any small R-value. Also if you are looking at R-values it's better to look for the weighted R-profile, because that is the value that fitting algorithms are typically minimizing. What I find most important is to watch the difference plot, when you have a decent measurement and the differences in this plot are approaching the noise level you are close to the best possible fit.
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