Profile fitting and Le Bail intensity extraction

• Nota Bene:: this feature is still in active development. Note: right now this only supports profile fitting with a pseudo-Voigt profile - support for the DE-PV profile used for TOF will be added later.
  
  

• To use profile fitting on a powder pattern you must first have for this pattern (i) a background component and (ii) defined a crystal phase contributing to this pattern (listed as

  PowderPatternDiffraction in the window).
  
  To begin profile fitting, the simplest way is to right-click on the powder pattern graph and select

  Fit profile + Le Bail extraction. Alternatively, you can either check the Profile Fitting (Le Bail) mode check box (see above), or use the profile menu in the PowderPatternDiffraction object. A menu will then appear:

• You can then check which profile parameters you want to optimize. It will then do 10 Le Bail cycles, followed by a series of profile fitting least squares refinement, with an increasing number of free parameters - depending on your choices. The optimization can be canceled using the progress dialog, and the results (Rwp and GoF are displayed in the log window - see the example above).

  
  
  After performing the profile fitting and the extraction,

  you must close the profile fitting window if you want to optimise the structure (in profile fitting mode the crystal structure is ignored).
  
  Once you have performed the extraction, you can

  display observed & difference Fourier maps in the 3D Crystal view.
  
  

  Note 1: as long as the Profile Fitting (Le Bail) mode box is checked, all pattern calculations will of course ignore the actual crystal structure. So if you want to optimize a crystal structure, you must first un-check this first !
  
  

  Note 2: the default in Fox is to optimize only the lower parts of the powder pattern first. The drawback of this approach is tha the angle-dependent parameters can go wrong - typically U,V,W width parameters which cause negative width at high angle. In case of a problem when increasing the calculation limit, you should reset the U and V parameters to zero and refine them again. Or you can change the max sin(theta)/lambda to include the complete powder pattern in the optimization.