# [Ifeffit] Linear Combination Fit

Shelly Kelly dr.sdkelly at gmail.com
Tue May 10 12:28:34 CDT 2011

```Hi Saugata

With appropriate standards, the sum of scaling factors equals 1, so that the
sum of the fractions of all
chemical species of an element equals the relative amount of the element in
the sample.
Physically, the spectra from a standard might contain more atomic scale
order than the representation
of that component. Structural disorder could be represented in the XANES
spectra by a broadening of the spectral line shape relative to the standard
spectrum. This mismatch between the standard spectrum and the
analogous species can be partially accounted for by relaxing the summation
constraint. In this case, the fitted scaling factors for the appropriate
standards are
renormalized to one, so they are intended to represent the approximate
fraction of each
species in the sample.

This is part of my book chapter. The next sections show some examples. If
you want a copy just send me an email directly and I'll send it to you.

Kelly, S. D., Hesterberg, D. and Ravel, B. (2008). Analysis of soils and
minerals using X-ray absorption spectroscopy. Methods of soil analysis, Part
5 -Mineralogical methods. Ulery, A. L. and Drees, L. R. Madison, WI, USA,
Soil Science Society of America: 367-463.

Cheers,
Shelly
dr.sdkelly at gmail.com

On Tue, May 10, 2011 at 12:01 AM, Saugata Datta <saugatadatta at hotmail.com>wrote:

>  Dear Iffefit group.,
>
> I am just starting to know this forum, and I read some messages from time
> to time and find it very useful., I have a question on the Linear
> Combination Fitting--using to fit my sample with a few standards.
> I am experiencing that on some iterations of the fit (which gives good
> reduced chi square value, / good R Factor values) but shows  the following,
> as an example:
> Standard  Weight                             E0
> X             0.267(0.056)                     0
> Y              0.249 (0.017)                   0
> M             0.220 (0.015)                   0
> N             0.428 (0.055)                   0
> P             0.000 (0.082)                   0
>
>  should I even choose this iteration, or will go to the the next one?
>
> And the next question is: if the addition of all weigths is 0.999 or 1.164
> --- can I consider them? What I mean is: what is the range of acceptance of
> sum of all weights (I am chqing the check box for force weights to sum to
> 1)?
>
> thanks for your anticipated help.
>
> saugata
>
>
>
>
>
> > Date: Mon, 9 May 2011 15:19:05 -0700
> > From: garcia.ff.000 at gmail.com
> > To: ifeffit at millenia.cars.aps.anl.gov
> > Subject: [Ifeffit] Linux command line ff2chi yields no output
> >
> > Dear users,
> >
> > I was able to install iffefit on linux. From the command line I run:
> >
> > feff6 feff.inp
> >
> > This worked fine and several feffnnnn.dat files were generated. Then,
> > I wrote an input script, tmp.iff (shortened list of paths here), for
> > ifeffit as follows:
> >
> > # tmp.iff
> >
> > path(1, file=feff0001.dat, s02 = 0.9, sigma2 = 0 .001)
> > path(2, file=feff0002.dat, s02 = 0.9, sigma2 = 0 .001)
> > path(3, file=feff0003.dat, s02 = 0.9, sigma2 = 0 .001)
> > path(4, file=feff0004.dat, s02 = 0.9, sigma2 = 0 .001)
> > path(5, file=feff0005.dat, s02 = 0.9, sigma2 = 0 .001)
> > path(6, file=feff0006.dat, s02 = 0.9, sigma2 = 0 .001)
> > path(7, file=feff0007.dat, s02 = 0.9, sigma2 = 0 .001)
> > path(8, file=feff0008.dat, s02 = 0.9, sigma2 = 0 .001)
> > path(9, file=feff0009.dat, s02 = 0.9, sigma2 = 0 .001)
> > path(10, file=feff0010.dat, s02 = 0.9, sigma2 = 0 .001)
> > path(11, file=feff0011.dat, s02 = 0.9, sigma2 = 0 .001)
> >
> > ff2chi(1-11, group=mycalc)
> >
> > fftf(mycalc.chi, kmin=1, kmax=15, dk=0.5, kweight=2.0, kwindow='hanning')
> >
> > #
> >
> > My aim here is to sum the paths to generate chi(k). Now if I run the
> > following command:
> >
> > ifeffit -x tmp.iff
> >
> > the following output is printed on the screen:
> >
> >
> > It appears that the feffnnnn.dat files were read successfully.
> > However, no mycalc.chi output was produced by ff2chi() [and therefore
> > no mycalc.chir_* output was produced by fftf()]. I don't know if my
> > approach is missing an important step or my entire procedure is
> > nonsensical.
> >
> >
> > Thanks a lot!
> > _______________________________________________
> > Ifeffit mailing list
> > Ifeffit at millenia.cars.aps.anl.gov
> > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>
>
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