Alan Hewat wrote:
Should one first refine lattice parameters and then "fix" them before
proceeding with structure
refinement?
In the early stages of a Rietveld refinement you might want to fix some
parameters, for example
you might want to refine just zero point, cell constants, scale factor etc to
get them
approximately right before refining the structural parameters as well. But if
you don't refine
all parameters together, you neglect some of the correlations between them, and
you will
under-estimate errors. The calculated standard deviations are correct only if
your model, with
the parameters you refine, is actually capable of describing the true structure.
Don't forget the profile parameters. Even with barely noticeable axial divergence, the peak position
will _NOT_ be at the point of highest intensity.
Larry
