Re: [Ifeffit] 1. Re xanes feff8 sulfur pyrite

Hi Josh, i have made two calculations respectively pyrite. You can see the results in the postscript file. The first (A) plot is from your pyrite.dat, the second plot is based on your feff.inp but recalculated on my Computer. The last (C) plot is based on my own crystallographic data (spacegroup p 2_1 /a -3) and feff.inp (attached as eck-feff.inp) file, maybe the same crystallographic data you used? With my feff.inp i can approve all of your atom-positions with the exception of atom 11 in your list respectively atom Fe3 in my list. But the results in the diagramm are nearly the same. The third file (feff.inp) is again your feff.inp file you sent to me.

Hi Josh,

thanks for your help and attached files. I will test your feff.inp files and compare the results.

cheers, Eckhard

Hi Eckhard, Try the attatched feff.inp files (gypsum.inp and pyrite.inp). I find that these produce different spectra with edges at ~2468.5 - gypsum ~2469.0 - pyrite

If you use do not get the same results, then there is something wrong with the code and we will have some debugging to do.

Also, if there are multiple sulfur sites in the material which have different local structure, you will need to do a configurational average by running with each site as the absorbing atom and averaging the signals. Cheers, Josh

P.S. I am also sending the result (gypsum.dat and pyrite.dat) so that you can compare.

On Tue, 16 Oct 2007, ifeffit-request@millenia.cars.aps.anl.gov wrote:

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Today's Topics:

1. Re xanes feff8 sulfur (Kelly, Shelly D.) 2. Re: Re xanes feff8 sulfur (s440697@stud.uni-goettingen.de)

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Message: 1 Date: Mon, 15 Oct 2007 15:18:14 -0500 From: "Kelly, Shelly D." Subject: [Ifeffit] Re xanes feff8 sulfur To: "XAFS Analysis using Ifeffit"

Cc: "John J. Rehr" , John Katsoudas

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Hi Eckard,

I realize that you have posted a message every month for about 3 months in a row without any reply: Shame on us... I will try to answer some of your questions and maybe that will help to get some discussion going. The energy scale in feff8 is NOT defined as you would expect it to be for determining the absolute energy of an edge. The energy scale in FEFF8 is related to the difference between the energy level of the intersist (potential level inbetween the muffin tins that represent atoms) and the threshold energy level for the excitation of the electron.

I realize that this doesn't solve your problem, but hopefully it will spark some discussion.

Cheers,

Shelly

Mon Aug 13 06:00:19 CDT 2007 Does anybody know a person, who has experience respective the topics xanes+feff8 and sulfur K-Edges? I would be very thankful for an answer :-)

sincerely yours, Eckhard Bosman

Tue Jul 10 10:07:38 CDT 2007

Hello,

i have problems with feff-xanes calculations related to pyrite. I try to get the k-edge of sulfur (as absorber) in FeS2. I get the edge at ~2472 eV and i think this is wrong because i get the same energy with gypsum and i think there should be an energyshift related to 2472 eV. My proceeding is as follows:

calculate the atomic positions with the asymetric unit from the http://rruff.geo.arizona.edu/AMS/amcsd.php database (Pyrite spacegroup Pa3) respectively http://rruff.geo.arizona.edu/AMS/xtal_data/CIFfiles/00596.cif with "powdercell 2.4"

feffrun with the feff.inp-file like in the attachment (thanks to Josh Kas for his feff-hints)

I started the feff-run on the one hand with 12 atoms (unitcell) and on the other hand with 22 atoms (14x Fe and 8x S in the cube)

After this i plotted from xmu.dat the absorbtion mu (column 4) as a function of the energy (column 1). The result is in the attachment too.

I don't know why i get everytime the Sulfur-k-edge at the same position (for pyrite or gypsum) respectively without energyshift related to 2472 eV.

many thanks for your help :-) Ciao, Eckhard

Fri Jun 15 08:48:21 CDT 2007

Hallo @all,

(first at all, sorry for my bad english)

i'm a student working on my diploma thesis (nexafs/xanes) and my job is to simulate with FEFF 8.4 spectra, for example absorption as a function of energy (mu_(E)). I'm a newbie in this topic and i tried to get the k-edge of Sulfur for the substance gypsum (CaSO4 * 2(H2O)) and pyrite (FeS2). I'm interested in the XANES-range of the spectra not the EXAFS. I get everytime my peaks at ~2472 eV for Sulfur as absorber whatever substance i use (gypsum, pyrite,...). There are no differences with the peak position on the energy-scale or shifts. I'm really confused :-( I think, there should be differences in the spectra... I send you two feff.inp files from my feff-runs. My source is the mineralogy database (http://rruff.geo.arizona.edu/AMS/amcsd.php) where i get the data for the unitcell. Then i put the data in the XtalDraw program to get the positions of the Atoms in Angstrom, by the way i get i nice 3D-View of the unitcell :-). Then i put the values of the positions into feff... I simulated pyrite with 12 atoms and gypsum with 48. I'm appreciative for every help :-)

ciao, Eckhard