Re: X-Fit and SPVII, FWHM?

Carsten Schinzer ( schinzer@icmcb.u-bordeaux.fr )
Thu, 17 Sep 1998 16:35:58 +0200

Sue wrote:

>PS Rietveld refinement is one of those few fields of intellectual endeavour
>wherein the more one does it, the less one understands.

Hm, hm,

I fully agree to that. Unfortnately, we have to admit, that currently
Rietveld refinements still require a huge amount of time to get into the
stuff and to "controll" the process instead of tumbling through it, hoping
nothing will go wrong ... though - it is far from being easily applicable
to whatsoever crystallographic problem ;-)

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I remember trying to use asymmetry correction in FullProf and starting fromzero values for the two parameters. It didn't work. I do use anothersoftware (SIMREF) that is even more susceptible (I consider FullProf areally stable program in terms of tolerance of "raw" starting parameters).However, giving the software a tiny "hint" where I want it to go (e.g. bysetting a starting value to 0.0001 instead of zero) often leads to astabilization of the refinement.

You might try to set one of your profile parameters just slightly differentfrom the other and see how things go.

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E-mails will come over me now, saying that this might lead to wrong minimaetcetc. You will sure tell me, that all this stuff is *NOT* mysterious; Ido sometimes think it is !Any comments welcome... especially those about mysteries of Rietvelding =:-)

Carsten

Carsten Schinzer ---------------------------------------

Institut de Chimie de la Matiere Condensee de Bordeaux 87, Avenue du Docteur A. Schweitzer F-33608 PESSAC fon +33 556 84 2650 (poste 7397) fax +33 556 84 2761 http://www.icmcb.u-bordeaux.fr/~schinzer--------------------------------------------------------