Re: Is it possible in GSAS to control the value of certain
parameters in a... For example, Uiso>0, 0<F<1, etc
No. Nor would you want to do this.
When Uiso or Occupancy refine to non-physical numbers (particularly
with neutron data) there is a implicit message that your model is not
fitting your data properly or you are using too many parameters. You
want to pay attention to this, not sweep it under the rug by adding a
constraint to the fit to hide the problem. There are occasions when
Uiso values cannot be modeled in Rietveld. In these cases one should
constrain the parameter by not refining it (and explaining why this
was needed in the associated publication.) More common is to group
Uiso parameters or fix background parameters. One may want to
constrain the sum of occupancies, but I see no reason to ever
constrain F > 0.
Brian
