Re: [Ifeffit] Linear Combination Fit

Dear Dr. Kelly, this was not my question in the first place, but I am still super interested in your book/book chapter on LC fitting. Would you send me a pdf-copy as well? Thanks so much, I am learning a lot through the ifeffit mailing list! Cheers Christoph

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@gmail.com

On Tue, May 10, 2011 at 12:01 AM, Saugata Datta 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

Now, I am confused about this "P" standard...as it shows 0.000 (weight); 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@gmail.com To: ifeffit@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:

reading feff0101.dat reading feff0102.dat reading feff0103.dat reading feff0104.dat reading feff0105.dat reading feff0106.dat reading feff0107.dat reading feff0108.dat reading feff0109.dat reading feff0001.dat reading feff0002.dat reading feff0003.dat reading feff0004.dat reading feff0005.dat reading feff0006.dat reading feff0007.dat reading feff0008.dat reading feff0009.dat reading feff0010.dat reading feff0011.dat

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@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

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-- Christoph Sahle Technische Universität Dortmund Experimentelle Physik I Otto-Hahn-Strasse 4 44221 Dortmund Germany Tel.: 0231-755-3759