Re: xfit/koalariet

L. Cranswick ( L.M.D.Cranswick@dl.ac.uk )
Thu, 27 Aug 1998 00:46:21 +0100 (BST)

>
> I am trying to import diffraction patterns using the *.XDD format
> (Easily translated from the JADE *.MDI output) into XFIT, but I have a
> problem determining what diffractometer settings to use for the fit. The
> data were collected by two methods: 1) a Phillips diffractometer with a
> constant theta slit and 2) as digitized Debye-Scherrer and Guinier
> films.
>
> How do I set the Axial Divergence and other factors for the constant
> theta slit?
>
> If anyone has any experience in these areas and can give me some advice,
> it would save my attempting lots of "trial-and-error" runs.

Examples of using both empirical peak fitting and Fundamental Parameters
peak fitting are at:
http://www.ccp14.ac.uk/tutorial/xfit-95/liti/empirical.htm
http://www.ccp14.ac.uk/tutorial/xfit-95/liti/rwfunpar.htm

Plus general tutorial information at:
http://www.ccp14.ac.uk/tutorial/xfit-95/xfit.htm

You will need to know the slit settings and Soller Slit acceptance
angles (Sollers are usually 5.1 degrees for Philips 1050 systems)

----

My personal experience is that FP peak fitting is tedious with XFIT
which is why many people do not go beyond using the Pseudo Voight or
Split Pearson function.

Though on lab data for indexing porposes - I usually go for FP peak
fitting to try and get a better idea on what possible overlap could
be present.

---

For quick fitting of data - using the empirical approach is quiteeffective.

> What settings should I use for a synthetic diffractogram derived from a> film?

Trying empirical peak fitting using XFIT might give you the leastgrief.

Using Split Pearson or Pseudo Voight should work. Though I do notbelieve there is a 100% kosher way of using FP on this data usingXFIT - though you could probably fudge a fit(?).

For modelling a nasty background - just fit this using broad pseudo voight peaks.

---

While I don't believe a "Peak fitting" version of BGMN is readyyet (called EFLECH based on the BGMN web site) - BGMN seems more advanced in modelling non-Bragg Brentano geometry peaks using FP methods.

Refer: http://www.mineral.tu-freiberg.de/mineralogie/bgmn/ger.html http://www.ccp14.ac.uk/ccp/web-mirrors/bgmn/mineralogie/bgmn/ger.html Lachlan.

-- Lachlan M. D. CranswickCollaborative Computational Project No 14 (CCP14)    for Single Crystal and Powder DiffractionDaresbury Laboratory, Warrington, WA4 4AD U.KTel: +44-1925-603703  Fax: +44-1925-603124  E-mail: l.cranswick@dl.ac.uk  Ext: 3703  Room C14NEW CCP14 Web Domain (Under heavy construction):                           http://www.ccp14.ac.uk