- Ifeffit - millenia.cars.aps.anl.gov

Re: [Ifeffit] SCF and FMS radius
by Feng Wang 12 Jan '09

12 Jan '09

Bruce and Eugenio, It is generally believed that the cluster size (or called spatial resolution) is mainly limited by MFP, to around 1 nm (in the near-edge region), but further spatial limitation may come from elastic scattering (i.e. through phase cancellation). This is what we tried to understand through FEFF calculations in one paper. I put the abstract here in case you want to check: We have investigated the factors that determine the degree of localization of the information obtainable from electron energy loss or x-ray absorption fine structure. Inelastic scattering of the excited core electron limits the volume of specimen contributing to the backscattered intensity to a diameter in the range of 12 nm, dependent on the excited-electron energy and the composition and crystal structure of the sample. Phase cancellation between the backscattered waves further reduces the effective diameter that determines the observed fine structure to below 1 nm. Since the spatial resolution attainable by transmission electron microscopy can approach 0.2 nm or can even be below 0.1 nm (with aberration correction), we predict that delocalization arising from the excited-electron range may limit the resolution of images based on changes in core-loss fine structure. (J. Appl. Phys. 104, 034906 (2008)). Feng > On Sunday 11 January 2009 12:23:26 pm Eugenio Otal wrote: > > I am simulating the XANES spectra of a erbium atom in an interstitial site > > of ZnO. I needed a SCF radius of 9.75 (316 atoms) and FMS radius of 11.90 > > (599 atoms) to obtain no change in the simulated spectra (differences of > > 0.01% or less) > > Now I am trying to simulate Er(OH)3 and it is using SCF 10.90 (622 atoms) > > and I still haven found convergence, I will need more even larger radius > > for FMS. > > Does the XAS phenomena have this distances? Has this distances physical > > meaning? > > Eugenio, > > The mean free path is quite long just above the Fermi energy. It is > conceivable that, in a well ordered material, the cluster size required for > convergence can be quite large. I believe that a very large cluster -- > something like 13 A -- is needed for pure silicon. Of course, I doubt that > erbium hydroxide is that well-ordered! > > So, are you are seeing physics associated with the mean free path or a problem > in Feff's construction of the potentials? I'm afraid I don't know how to > answer that, but hopefully John or one of his gang will weigh in. Do you see > the changes larger than your threshold over the entire data range or only > very close to the edge? > > Good luck, > B > > -- > > Bruce Ravel ------------------------------------ bravel(a)bnl.gov > > National Institute of Standards and Technology > Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 > Building 535A > Upton NY, 11973 > > My homepage: http://xafs.org/BruceRavel > EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/ > _______________________________________________ > Ifeffit mailing list > Ifeffit(a)millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit ==================================== National Institute for Nanotechnology 11421 Saskatachewan Drive Edmonton, Canada T6G 2M9

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How to get the accurate fittting results from the fit in Artemis
by abhijeet gaur 12 Jan '09

12 Jan '09

Hi Actually I trying to learn the fitting procedure in Artemis but I am not getting the actual bond length in the fit results of artemis . So I want to know that that how to get actual parameter from Artemis.And how to exploit the result of Artemis.

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Query regarding error bars
by Bindu R. 09 Jan '09

09 Jan '09

Hi all, Could any tell me in a simple language about the error bars returned by the EXAFS fitting program? what do they exactly represent?How is it determined?How is the number of iterations decided.In addition to R-factor what are the other parameters which determines a good fit.For a R-factor ~0.001, if the value of chi2~10,000 and reduced chi2 ~ 500, can one consider the fit to be good even if one gets a good match to the experimental spectra. Bindu Dr.Bindu R. Visiting Fellow BG-37 DCMP&MS Tata Institute of Fundamental Research Homi Bhabha Road Colaba Mumbai-400 005 India Contact Number Lab- 022-2278 2256, 022-2278 2671 Mobile-919892536830 Add more friends to your messenger and enjoy! Go to http://messenger.yahoo.com/invite/

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Re: [Ifeffit] posting to the ifeffit mailing list
by JeongEunSuk 07 Jan '09

07 Jan '09

Hello Bruce Ravel I have another questions. I got the charge transfer of TiO2 from FEFF8 as following;Ti: (not absorber) Charge transfer : 0.556 Electron counts for each orbital momentum: 0 0.408 1 6.678 2 2.350 3 0.000O: Charge transfer : -0.280 Electron counts for each orbital momentum: 0 1.843 1 4.354 2 0.087 3 0.000It is known that the electron number of Ti atom ( the atomic number 22) is 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^2. In the results of FEFF, 0 is s orbital, 1 is p orbital so on.. right? as you know, there is each s-orbital or p-orbital in principal quantum number.which orbital momentum of principle quantum number does 0, 1, 2 and 3 mean? second I cant understand electron counts. I thought that Charge transfer was calculated by electron counts for each orbital momentum, comparing the electron counts of free atom.So I tried to calculate like this: In free oxygen atom case, 2^s has 2 electron, 2^p! has 4 electron. The electron counts calculated by FEFF8 is 1.843 + 4.354 + 0.087 =6.284So charge transfer is 6 - 6.284 = 0.284 The charge thransfer, 0.284, obtained from my calculation is different from the value of FEFF8. How can I get charge transfer form electron counts? > From: bravel(a)bnl.gov> To: eunsuk1986(a)hotmail.com> Subject: posting to the ifeffit mailing list> Date: Mon, 5 Jan 2009 17:10:31 -0500> > > Hi Jeong,> > I think I know what went wrong with your post to the mailing list from last > Friday. I think that you (for some reason) sent the mail to> ifeffit-bounces(a)millenia.cars.aps.anl.gov> rather than to> ifeffit(a)millenia.cars.aps.anl.gov> > The second address is the normal point of entry to the mailing list. The > other address is part of the mailing list administration. I am not sure how > you ended up sending email there. Weird. If you make sure to send your mail > to the second address, it should get posted without any problems.> > If you do have any problems posting to the mailing list, I will probably be > notified automatically. But if you attempt to send mail to the mailing list > and have any problems, please let me know as soon as possible so I can try to > correct the problem.> > Regards,> B> > -- > > Bruce Ravel -------! ----------------------------- bravel(a)bnl.gov> > National Institute of Standards and Technology> Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2> Building 535A> Upton NY, 11973> > My homepage: http://xafs.org/BruceRavel> EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/ _________________________________________________________________ 블로그에 윈도우 라이브 메신저(베타)를 홍보하면 선물을 드립니다! http://windowslive.msn.co.kr/wlm/customer/view.asp?sectionDiv=2&seq=272

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charge transfer
by Bruce Ravel 05 Jan '09

05 Jan '09

Hi all, The following message from Jeong Eun Suk was not delivered correctly to the mailing list. Fortunately, I noticed the problem and am forwarding it along now. B Original message: what does charge transfer mean in FEFF? I cant understand what the number of charge transfer like 0.058, -0.073 means. The number indicate the number of electron in atom? If anybody knows it, please answer Charge transfer: iph charge(iph) 0 0.058 1 -0.073 2 0.072 -- Bruce Ravel ------------------------------------ bravel(a)bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/

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Problem running Feff through Artemis on Mac OS
by Aaron Slowey 02 Jan '09

02 Jan '09

Hello, I have Artemis running on intel Mac OS 10.4 and am unable to get FEFF to run by using Artemis. I have changed the preferences in the 'atoms' submenu to have feff_version as 7 and template as feff7 and then I have, under the 'feff' submenu, the path to my feff executable, specifically "/Users/aslowey/feff/feff7.exe" I tried removing the .exe -- no go. Then I reverted back to Artemis' default settings (feff version 6) and it still didn't work. I relocated both the feff.inp and feff executable in the same folder, but this also failed. In all cases, the Artemis palettes window opens to the Messages tab with red text that Artemis configured incorrectly...incorrect value of feff->feff_executable. Is there something about Mac OS that FEFF can't work? - Aaron Slowey

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subscription
by 穆鑫 29 Dec '08

29 Dec '08

Hello: I want to subscribe the Ifeffit . Thanks! Happy New year!

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How to identify N and O atoms in the first coordinate
by mzhu＠udel.edu 22 Dec '08

22 Dec '08

Hello all, Merry Christmas! I have some samples of heavy metal sorption on bacterial biofilm. I want to figure out what elements are coordinated with the heavy metal in the first coordinate. Since the oxygen and nitrogen have similar scattering factors, how can I differetiate them? Using shell-by-shell fitting or linear combination fitting with standards? Thanks. Best wishes, Mengqiang Zhu ----------------------- Mengqiang Zhu Ph.D Candidate Environmental Soil Chemistry Department of Plant and Soil Sciences University of Delaware 152 Townsend Hall Newark, DE 19716 http://ag.udel.edu/soilchem/zhu.html

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Re: [Ifeffit] How to identify N and O atoms in the first coordinate
by Frenkel, Anatoly 20 Dec '08

20 Dec '08

The fact that PCA tells between known Ni-N and Ni-O complexes by adding one more component when the wrong complex is added (N to O or vice versa) does not mean that there is specific fingerprinting sensitivity to N or O. One needs to demonstrate first that all Ni-N pairs have similar distances and disorder, regardless of their chemical surrounding, and that the same is true for Ni-O. Only in that case your PCA results indeed mean that the Ni sorbed biofilm have both types of bonds. Otherwise you cannot prove that it is Ni-N plus Ni-O vs. a situation where there are two unique types of Ni-O that have not been matched to your Ni-O standard and may thus fool you in thinking that one of them is due to Ni-N instead. Thus, before you conclude that, you should verify whether various Ni-N and Ni-O complexes have same pair properties. From your description it appears not to be the case since you have two components (not one) for your oxygen ligands and nitrogen ligands. Anatoly ----- Original Message ----- From: ifeffit-bounces(a)millenia.cars.aps.anl.gov <ifeffit-bounces(a)millenia.cars.aps.anl.gov> To: XAFS Analysis using Ifeffit <ifeffit(a)millenia.cars.aps.anl.gov> Sent: Fri Dec 19 18:39:24 2008 Subject: Re: [Ifeffit] How to identify N and O atoms in the first coordinate Hello Anatoly, Thanks for your reply. I could not do it as the literature you mentioned since I do not have detailed structural information as they do. I am wondering if the following method can be justified to indentify nitrogen atoms: 1) EXAFS data of 7 nickel oxygen-coordinated organic and inorganic complexes in which nickel only coordinates to oxygen atoms from carboxyl group, phosphoryl group and water molecules. 2) Fourier back transformation of the peak from 1-2 aus. in R+ delta-R space. This R range must cover the scattering peaks from both nitrogen and oxygen. Then chi functions of these complexes are obtained. 3) A principal component anlaysis (PCA) was performed over the oxygen-coordinated dataset of the chi functions obtained in the step (2). PCA analysis indicated two major components based on the IND values. 4)Then chi functions of two nitrogen-coordinated nickel complexes was obtained using the same method as step 2). It is certain that nitrogen atoms are coordinated to the nickel in the first shell in addition to oxygen atoms. 5) A target transformaiton of the chi function of two nitrogen-coordinated nickel complexes using oxygen-coordianted dataset resulted in the SPOIL values close to 5. Addition of one of the two complexes to the group of nickel complexes in PCA, PCA resulted in 3 components. These indicate that they have different coordination environment to the oxygen-coordinated nickel complexes. It is expected because they have nitrogen in the first shell. 6) A target transformation conducted on a sample of nickel-sorbed biofilm (back fourier transformed chi function in 1-2 aus.) resulted in the value close to 5. It means that the sample can not be represented by the nickel organic group, either. Since the first shell only can have two types of atoms, oxgen and nitrogen. If the nickel sorbed on biofilm can not be represented by the nickel oxygen-coordinated organic group which only has oxygen in the frist shell, it must have nitrogen atoms in the first shell. Also, linear square fitting of the Ni_biofilm with the nitrogen-coordinated complexes resulted in the better goodness than other oxygen-coordinated complexes. Thus, the nitrogen must exist in the first shell of Ni_biofilm sample. Do you think this method is reasonable? Best wishes, Mengqiang Zhu ----------------------- Mengqiang Zhu Ph.D Candidate Environmental Soil Chemistry Department of Plant and Soil Sciences University of Delaware 152 Townsend Hall Newark, DE 19716 http://ag.udel.edu/soilchem/zhu.html ---- Original message ---- >Date: Fri, 19 Dec 2008 16:34:36 -0500 >From: ifeffit-bounces(a)millenia.cars.aps.anl.gov (on behalf of "Frenkel, Anatoly" <frenkel(a)bnl.gov>) >Subject: Re: [Ifeffit] How to identify N and O atoms in the first coordinate >To: "XAFS Analysis using Ifeffit" <ifeffit(a)millenia.cars.aps.anl.gov>, <ifeffit(a)millenia.cars.aps.anl.gov> > >Dear Mengqiang, > >To the best of my knowledge, in most cases Nitrogen cannot be discerned from Oxygen as a nearest neighbor since their scattering properties are similar. Thus, if you want to solve an "inverse" problem ("Which type of neighbors do I have") you cannot do it. However, if you believe you have some knowledge about the type of metal-oxygen bonding: either M=O or a M-O or a M-OH or a M-OH2 (the first one is the shortest and the strongest, the others may have similar interatomic distances but different bond strengths), you can advance somewhat. > >If you have a certain number of distinct models you want to compare the data against, it can be done via a linear combination fitting, or by direct algebraic extraction of any given type of the pair contribution from the data, as described, for example here: > >E. Poverenov, I. Efremenko, A. I. Frenkel, Y. Ben-David, L. J. W. Shimon, G. Leitus, J. M. L. Marin, D. Milstein. A terminal Pt(IV)-oxo complex bearing no stabilizing electron withdrawing ligands and exhibiting diverse reactivity. Nature 255, 1093-1096, 2008. > >See supplementary info to that article for specific details. >Regards, >Anatoly > > >________________________________ > >From: ifeffit-bounces(a)millenia.cars.aps.anl.gov on behalf of mzhu(a)udel.edu >Sent: Fri 12/19/2008 4:20 PM >To: ifeffit(a)millenia.cars.aps.anl.gov >Subject: [Ifeffit] How to identify N and O atoms in the first coordinate > > > >Hello all, > Merry Christmas! > I have some samples of heavy metal sorption on bacterial biofilm. I want to figure out what elements are coordinated with the heavy metal in the first coordinate. Since the oxygen and nitrogen have similar scattering factors, how can I differetiate them? Using shell-by-shell fitting or linear combination fitting with standards? Thanks. > >Best wishes, > >Mengqiang Zhu > > > > > > > >----------------------- >Mengqiang Zhu >Ph.D Candidate >Environmental Soil Chemistry >Department of Plant and Soil Sciences >University of Delaware >152 Townsend Hall >Newark, DE 19716 >http://ag.udel.edu/soilchem/zhu.html >_______________________________________________ >Ifeffit mailing list >Ifeffit(a)millenia.cars.aps.anl.gov >http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > > > >_______________________________________________ >Ifeffit mailing list >Ifeffit(a)millenia.cars.aps.anl.gov >http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit _______________________________________________ Ifeffit mailing list Ifeffit(a)millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

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Re: [Ifeffit] Problems with feff and crystallographic data (Now with bug report)
by Gregory Merchan 19 Dec '08

19 Dec '08

Hi Hashem, Atoms doesn't handle the occupancy data in the CIF file. See this page for more info: http://cars9.uchicago.edu/iffwiki/FAQ/FeffitModeling#head-b273ecfd19542ec82… I assume you see a message like this one that I see: This warning indicates a problem in the Atoms list. For some reason you have atoms that are separated by than 0.93 Angstroms (or 1.75 Rydberg). If you look on the Atoms tab in Artemis when you open the CIF file, you should see that the co-ordinates for Mg and Al are all 0.00000 ; i.e., all Atoms sees is that they are in the same place. Bruce, here's two bug reports: 1. The warning message above is missing the word "less", as in "separated by _less_ than 0.93 Angstroms" 2. It's an extensive message but doesn't mention this kind of problem. If you want to drive yourself mad with interface stuff, you could catch and highlight these errors on input and disable the controls they affect until the input is corrected. A tricky part of that is making sure the user knows what the highlighting means and has a clue about how to fix the error without - say - throwing up a talking paperclip. A sort of "heavy tooltip" ("lead balloon"?) could be shown - placed so as not to obscure the relevant controls - with a brief message, a way to get to the more help, and dismissal button. An automatic fade out might be nice, not sure. So long as the bad input exists, there should be a way to get the message back, like mousing over the highlighted input or the disabled controls. I don't know of any cross-platform toolkit that makes that kind of thing easy. Cheers, Greg On Thu, Dec 18, 2008 at 10:04 PM, Hashem Stietiya <mstiet2(a)lsu.edu> wrote: > Hello! > > > > I was using Artemis to run feff and generate paths from hydrotalcite. > However, it failed to run and an error message indicated that there is > something wrong with the crystallographic data. I used the crystallographic > data of hydrotalcite from different sources, but encountered the same > problem. Can you please help identify the problem and run feff? > > > > Please find attached the crystallographic data for hydrotalcite. > > > > I appreciate your help. > > > > Regards, > > Hashem Stietiya > > Louisiana State University > > > > _______________________________________________ > Ifeffit mailing list > Ifeffit(a)millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > >

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