Is the fundamental parameter approach better thanPerhaps someone is about to explain the difference is between "fundamental parameters" and anything else? I used to think it might mean convoluting something which was actually measured into the peakshape description, but this doesn't always seem to be the case? I'm guessing it has to be more than choosing suitable equations for peak width parameters and peak positions as a function of scattering variable, otherwise all programs are using fundamental parameters already, just some are better approximations for certain diffractometers than others.
mathematical approach used in most of the Rietveld
refinement programs?
In any case, if the calculated peakshape matches the observed peakshape then it makes no difference for refinement of a crystal structure. For deriving microstructural parameters, like "size" and "strain", then a better description of the instrument can help, and can be a good indicator of diffractometer misalignment. In that sense, zero shift is a fundamental parameter, but does not seem to be unique to "fundamental parameters" programs. Perhaps the difference is that programs which don't do "fundamental parameters" make you compute "size" and "strain" from the peakshape parameters yourself.
Jon
