> Your sample will probably broaden the lines (LX, LY, etc.) so much that
any attempt to vary the Gaussian
>coefficients will yield nonsense.
Just some remark (of course, I am not a great specialist):
At least to my experience, there is always some Gaussian broadening from
the sample as well, and (again it is my humble opinion only) at least U is
better to allow to be refined.
For example, Rietan manual states the problem in the following way:
{
U, V, and W tend to be highly correlated, with a result that various
combinations of quite different values can lead to essentially the
same variance, sigma^2. These three parameters, therefore, do not
converge in a stable manner when refined simultaneously (Prince,
1993). In particular, refining P in addition to U, V, and W almost
certainly affords a singular (non-positive definite) coefficient matrix.
Of the four profile-shape parameters in Eq. (5), V and W depend not on
specimens but only on instruments (Young & Desai, 1989). Then, these two
instrumental parameters may well be fixed at values obtained by the
Rietveld refinement of a well-crystallized sample where profile broadening
is negligible, i.e., P = 0 .
}
Sincerely, Maxim.
__________________________________
Maxim V. Lobanov
Department of Chemistry
Rutgers University
610 Taylor Rd
Piscataway, NJ 08854
Phone: (732) 445-3811
