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The LS Controls pane shows information about the current experiment, typically found in the EXPEDT "Least Squares Controls" options.
Note that the order that histograms appear in this pane is determined by the "Sort histograms by" option in the Options Menu.
In the extraction method developed by Armel LeBail, reflection intensities are "optimized" by treating the setting the Fcalc value for each reflection to the Fobs value extracted during the previous cycle. By iterating, the Fcalc values slowly converge to a set of reflection intensities that yields a best fit to the pattern. The Fobs values are determined every time GENLES is run, or a least squares refinement cycle is run. This it is possible to improve the LeBail fit, by running GENLES with the "Number of Cycles" set to zero.
Note that due to reflection overlap, there are usually many different ways to apportion intensities with fits of comparable quality, depending on what starting values are used for Fobs. Any time POWPREF is run, the reflection list is regenerated and the first time that GENLES is run, the starting Fcalc values are set one of two ways:
It is possible to refine unit cell, background, profile and other non-structural parameters at the same time as a LeBail extraction is performed. I often do this, for two reasons. One is that the final LeBail Rwp and Chi2 provides a better measure of the best possible fit than the statistical values, particularly if the material has non-ideal peak shapes or other factors that cannot modeled. The second reason is the LeBail fit provides excellent starting values for the unit cell, background and profile parameters, so these terms need not be refined again until all structural terms have been fit well.
These LeBail refinements, alas, are prone to diverge if the the extracted intensities are changing rapidly and other parameters, such as unit cell parameters are compensating. It is a good practice to run GENLES several times with the "Number of Cycles" set to zero each time POWPREF is run -- to allow the reflection intensities to converge before refining parameters.
Note that extraction different methods can be used for different phases in a histogram. It can be convenient to use LeBail extraction for an impurity phase, in the case where the impurity has preferred orientation or has a known unit cell, but an unknown structure. I have also used LeBail fits to obtain precise lattice constants via profile fits of materials where the exact structure is not known, so a Rietveld refinement cannot be performed.
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