Dear Sandra Moussa,
there is one program that could fit on it, it's Maud.
There are a couple of problems anywhere:
- superstructure cell broadening is actually treated by the Warren
theory and so only for hcp, bcc and fcc structures. Adding a model for
also your trigonal is a trivial task and takes a very short time
provided there is a mathematical formulation for it (actually I can add
it for you if you can provide me a mathematical model, something like
that give the extra broadening as a function of the hkl). Actually I
have not too much time to look for a model.
- only one type of peak is inside the program but the asymmetry is
handled in a much better way than in other programs (is a real
convolution as it should be) so I never found a pattern that I was not
able to fit very well with my function (from high resolution synchrotron
to neutron TOF). This is the reason I never added another function.
- f' and f'' must be added in a file outside the program not using the
interface, but in case I can provide you the instructions on how to do
that.
- there is no manual but only few tutorials and some examples. Indeed is
a interface based program with some automatic refining modes also.
In case you will need the new version (the one on the web is a little
bit outdated and the new one will be on line end of this week).
Basically the only problem I see is about a model for trigonal
superstructure broadening (I worked a lot with superstructure broadening
of intermetallics and I know that anisotropic models (like Popa, that's
included also) don't work sufficiently well with this kind of broadening
(that's the reason I have included the Warren theory previously
mentioned).
Best regards,
Luca Lutterotti
On Friday, June 22, 2001, at 02:07 PM, Mr L.D. Noailles wrote:
>
>
> Dear All,
>
> I have several synchrotron X-ray data sets collected at different
> wavelengths (as well as TOF neutron and standard Cu Xray radiation). The
> pattern of the single phase material I am trying to refine contains both
> strong sharp 'subcell' peaks and weak broad 'supercell' peaks.
>
> The subcell reflections are those allowed in R-3m and the supercell
> reflections are the extra reflections generated by lowering to P-3m
> (i.e. p-3m reflections -R-3m reflections)
>
> I would like to refine structures using a combination of all the data
> sets and account for both these types of reflections and also be able to
> include f' and f'' values.
>
> Therefore I'm looking for a "Rietveld" program that can deal with all
> the following options:-
>
> 1. At least two profile functions to fit the two types of peaks in each
> histogram, preferably by assigning reflection conditions for paticular
> classes of reflections to the paticular profile functions.
>
> 2. enable the use of multiple histograms (in particular with different
> wavelengths)
>
> 3. deal with anomalous scattering data ie able to input f' and f''.
>
> I have already looked at using GSAS and the constant wavelength profile
> function 3 which gives the option of using stacking vectors but so far
> have been unable to improve the fit of the broad reflections. I have
> also considered using Rietan and although it offers partial profile
> relaxation for a number of reflections and the capability of including
> f' and f'' it cannot handle multiple histograms with different
> wavelengths.
>
> Does such a program with the listed criteria, exist? Any suggestions or
> comments would be much appreciated.
>
> regards,
>
> Sandra Moussa
> Department of Chemistry
> Liverpool University
>
>
>
