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

Re: postdoc opening
by Matt Newville 07 Jan '05

07 Jan '05

Hi Folks, I get a fair number of questions and notices about jobs and post-doc opportunities related to XAFS. So far, I've been reluctant to use this list for that purpose, but since there are many grad students and post-docs on this list, it seems that posting these to the mailing list could help everyone. So, here's a notice for a post-doc fellowship at LBNL, sent to me from Corwin Booth (chbooth(a)lbl.gov) http://actinide.lbl.gov/gtsc/JobDetails.htm Corwin also wrote: > The final candidate will work closely with one or more group > members on something related to actinide research. The group is > an actinide chemistry group, however there are opportunities to > work in solid state physics. Somebody interested in x-ray > absorption spectroscopy, x-ray scattering and/or magnetism of > f-electron systems would obviously be great for me, and I am > starting to focus on measurements in diamond anvil cells. We > have high-radioactivity labs, as well, so someone interested in > synthesis of actinide intermetallics could also make big > contributions. There are other opportunities, so an interested > person could contact me. If you know of any potential > candidates I would appreciate you forwarding them the ad or this > email. We plan on filling this position ASAP. Good luck!! --Matt PS: if anyone else would like to post job notices here, feel free.

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Fwd: News
by Bruce Ravel 07 Jan '05

07 Jan '05

Hi Folks, Can anyone here help Michel with his problems installing the latest horae on his Mac? Thanks, B ---------- Forwarded Message ---------- Subject: News Date: Friday 07 January 2005 06:11 am From: Michel Jaouen <Michel.Jaouen(a)univ-poitiers.fr> To: ravel(a)phys.washington.edu Previously I have updated all using sudo horea_update. At that date (september 2004) it creates a folder horae-042 with the attached log file. It fixes the problems I have mentionned previously: all run fine (artemis version number 07.013, athena version number 08.035). I have seen your mail concerning a new update (horae-047). So I do as previously: sudo horea_update. I receive in the terminal window a lot of informations related to the instal and at the end all seems OK. But when I run artemis in a terminal X window, I have the same version as previously. Looking in the Ifeffit folder I don't see an horea-047 folder nor a log file. The only change I found are in the bin folder where I have new artemis and athena files that are labelled as executable unix files but I can open by clicing on them as text files! So what happens here: I miss something I guess, but what? Any hints? Cheers Michel PS I don't obtain the new interface as quoted on your web server, so I suspect I have some install to do "by hands", but why it is different from the previous update? ------------------------------------------------------- -- Bruce Ravel ----------------------------------- ravel(a)phys.washington.edu Code 6134, Building 3, Room 405 Naval Research Laboratory phone: (1) 202 767 2268 Washington DC 20375, USA fax: (1) 202 767 4642 NRL Synchrotron Radiation Consortium (NRL-SRC) Beamlines X11a, X11b, X23b National Synchrotron Light Source Brookhaven National Laboratory, Upton, NY 11973 My homepage: http://feff.phys.washington.edu/~ravel EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/

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Generating single scattering paths in Artemis
by Carlo U. Segre 06 Jan '05

06 Jan '05

Bruce: Occasionally, I don't know or don't care what the extended crystallographic environment of the absorber. All I want to do is apply single scattering analysis and I need some simple paths from FEFF. At this time, I can't see how to do this within Artemis since the Atoms page requires a space group and more information than I have available. Would it be possible to have the option for a simpler interface which just allows me to generate single scattering paths between two atoms at a specific distance from each other? Perhaps, I could even specify a coordination geometry (tetrahedral, octahedral, etc.)? Carlo -- Carlo U. Segre -- Professor of Physics Associate Dean for Special Projects, Graduate College Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 Carlo.Segre(a)iit.edu http://www.iit.edu/~segre

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Re: [Ifeffit] Generating single scattering paths in Artemis
by Frenkel, Anatoly 06 Jan '05

06 Jan '05

<<feff.inp>> Hello Carlo et al, FEFF6 allows to use SS cards that were specifically designed to calculate single-scattering paths in the case the structural details are not known, as in Carlo's case. I am attaching a working example where I used to calculate single scattering FEFF in Cu-O in octahedral coordination in Cu2+[H2O]6 complex. I included hydrogen in the input file since it affects charge on oxygen, but in principle it works. Some details are given in this article: http://pubweb.bnl.gov/people/frenkel/HUMIC-EXAFS/est.pdf You can run FEFF6 using attached file and note that it produces three files, each corresponds to the single shell of Cu-O atoms. Note the use of the OVERLAP card in the attached file, as well as the use of Bohr's radius to work around the bug in FEFF6 that uses distances in OVERLAP as multiples of Bohr's radius instead of Angstrems, while the units in SS card are in Angstrems. Regards, Anatoly Anatoly Frenkel, Ph.D. Associate Professor Department of Physics Yeshiva University 245 Lexington Avenue New York, NY 10016 http://www.yu.edu/faculty/afrenkel Office: tel. (212) 340-7827 fax (212) 340-7788 anatoly.frenkel(a)yu.edu Laboratory: tel. (631) 344-3013 frenkel(a)bnl.gov -----Original Message----- From: ifeffit-bounces(a)millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov]On Behalf Of Barton, David (DG) Sent: Wednesday, January 05, 2005 4:46 PM To: 'XAFS Analysis using Ifeffit' Subject: RE: [Ifeffit] Generating single scattering paths in Artemis Scott, > This can be fixed by editing the feff.inp file to remove the > Fe potential 1, but that's not enough--the oxygen scatterers > then have to have their potential renumbered to 1 to make > things work. That's a lot of work to do what should be simple. > > So I vote for changing the way Artemis works in such > circumstances so that less editing is needed: if the > absorbing atom is not present in the scattering list, then it > shouldn't have a second entry in the potential list. > I second this vote, since I also have had this same problem. New users could become quickly disgruntled by the Fatal Error message when attempting to put in simple systems or just by choosing a short cluster distance to only include the first shell in the FEFF calculation. At a minimum, it would be nice if Artemis trapped this error and reported a more friendly popup error message. Dave _________________________________ David Barton, PhD. The Dow Chemical Company Catalysis R&D _______________________________________________ Ifeffit mailing list Ifeffit(a)millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit <<feff.inp>>

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Re: Generating single scattering paths in Artemis
by Webb, Samuel M. 05 Jan '05

05 Jan '05

Hi all... I know that this isn't necessarily an Artemis solution, but there is an option/module in SIXPACK (that other IFEFFIT interface) to do just what you've been asking about -- create simple single scattering paths between two atoms in a variety of coordination environments (tetrahedral, octahedral, etc). It has a nice periodic table interface to boot. I use it occasionally to do some quick and dirty fitting -- I do agree with Scott that its not always the most accurate way to go about things. The resulting FEFF file is placed in a FEFF folder in the sixpack root directory. Hope that helps some. Sam

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RE: [Ifeffit] Generating single scattering paths in Artemis
by Barton, David (DG) 05 Jan '05

05 Jan '05

Scott, > This can be fixed by editing the feff.inp file to remove the > Fe potential 1, but that's not enough--the oxygen scatterers > then have to have their potential renumbered to 1 to make > things work. That's a lot of work to do what should be simple. > > So I vote for changing the way Artemis works in such > circumstances so that less editing is needed: if the > absorbing atom is not present in the scattering list, then it > shouldn't have a second entry in the potential list. > I second this vote, since I also have had this same problem. New users could become quickly disgruntled by the Fatal Error message when attempting to put in simple systems or just by choosing a short cluster distance to only include the first shell in the FEFF calculation. At a minimum, it would be nice if Artemis trapped this error and reported a more friendly popup error message. Dave _________________________________ David Barton, PhD. The Dow Chemical Company Catalysis R&D

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Athena & Artemis in Windows
by Peter Southon 22 Dec '04

22 Dec '04

Hello Windows people A few days ago Shelly suggested that Athena and Artemis don't work when installed in the directory "C:/program files/ifeffit/". This has always worked for me using XP, though I wouldn't be surprised if it caused problems in some earlier versions of Windows. Regarding Poorani's question about TRAP files, I have found it useful to put a shortcut to "C:/program files/ifeffit/horae/stash/ARTEMIS.TRAP" on my desktop or wherever for easy access. Cheers, Peter >Date: Fri, 11 Jun 2004 08:36:32 -0500 >From: "Kelly, Shelly D." <SKelly(a)anl.gov> >Subject: RE: [Ifeffit] Running FEFF >To: "XAFS Analysis using Ifeffit" <ifeffit(a)millenia.cars.aps.anl.gov> >Message-ID: <1C1577844A0BDF448E14E8CCB2F74424015A1B6D(a)ANLMAIL.anl.gov> >Content-Type: text/plain; charset="us-ascii" > >Hi Poorani, > >I believe that Athena and Artemis do not work properly when installed in >the C:/program files/ifeffit directory. The installation proceedures >say to specify C:/ifeffit instead. To fix if, but all of C:/program >files/ifeffit into the trash and then re-install. > >Shelly Peter Southon Post Doctoral Fellow School of Chemistry University of Sydney NSW 2006, Australia +61 2 9351 4425

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RE: [Ifeffit] Using more than one E0
by Kelly, Shelly D. 15 Dec '04

15 Dec '04

Hey Scott, One correction, I botched this part: > -----Original Message----- > From: Kelly, Shelly D. > Sent: Wednesday, December 15, 2004 10:06 AM > To: XAFS Analysis using Ifeffit > Subject: RE: [Ifeffit] Using more than one E0 > > Hi Scott, > > See below: > > The MS scheme you outline below seems to treat the E0 due to the > scattering species (I'll call that the "bonus" E0 for lack of a better > term) as being the average of the bonus E0's for all the scattering > atoms > in the path. Thus you give the Cu-O1-Cu1-Cu path as using the average of > the O1 and the Cu1 bonus E0's, while the Cu-O1-Cu-O1 path uses just the > O1 bonus E0. I would naively expect we should be using the sum, rather > than the average. After all, if this bonus E0 is a correction to the > shift caused by the muffin-tin potential FEFF has calculated, shouldn't > a > MS path that bounces off the same atom twice have to use twice the > correction? I feel like there's something basic I'm missing here... > > [Kelly, Shelly D.] The energy shift applies to the entire scattering > event. The scattering event can not be broken down into the sum of the > legs. [Kelly, Shelly D.] Most of the time, it is good to think about the scattering event as being a sum of the legs. If you follow this through you can see why the energy shift is an average rather than a sum. Take two sine waves and displace one from the other by a few eV. Then add them up. The total will have an energy shift that is in between the two that you started out with. --Hence an average rather than a sum. Hence the energy shift for the entire scattering event can be > approximated as an average of the energy shift from each leg. I have > used the average energy shift a lot and found that it works well. I > have never tried using a sum of the energy shifts... I think that in > an extreme limit you can convince yourself that the sum will break down > for an 8 legged paths. The energy shifts are "never" greater than 10 > eV. "never" in my experience. -Hence the answer to your next question. > > Also, what is your experience as to the actual differences in bonus E0's > that you get in ionic compounds? Right now one of my students is working > with Sr(NO3)2... should we really expect the difference in bonus E0's > between the Sr2+ and the oxygen atoms to be more than 12 eV, or does > some > kind of charge overlap from the nitrate ions actually make the strontium > ions behave as if they are less than +2? > > [Kelly, Shelly D.] One full electron of ionic bonding gives about 6 eV. > So that is about the most you would expect from different ions in a > solid. Usually, I have found 3 to 4 eV. You make up most of the > valence state change from the shift in the edge position. I have found > unrealistic energy shifts when I try to use too much chi(k) data at low > k. I'd look there first for you 12 eV shift. > > HTH > Shelly > > > _______________________________________________ > 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] Using more than one E0
by Kelly, Shelly D. 15 Dec '04

15 Dec '04

Hi Scott, See below: The MS scheme you outline below seems to treat the E0 due to the scattering species (I'll call that the "bonus" E0 for lack of a better term) as being the average of the bonus E0's for all the scattering atoms in the path. Thus you give the Cu-O1-Cu1-Cu path as using the average of the O1 and the Cu1 bonus E0's, while the Cu-O1-Cu-O1 path uses just the O1 bonus E0. I would naively expect we should be using the sum, rather than the average. After all, if this bonus E0 is a correction to the shift caused by the muffin-tin potential FEFF has calculated, shouldn't a MS path that bounces off the same atom twice have to use twice the correction? I feel like there's something basic I'm missing here... [Kelly, Shelly D.] The energy shift applies to the entire scattering event. The scattering event can not be broken down into the sum of the legs. Hence the energy shift for the entire scattering event can be approximated as an average of the energy shift from each leg. I have used the average energy shift a lot and found that it works well. I have never tried using a sum of the energy shifts... I think that in an extreme limit you can convince yourself that the sum will break down for an 8 legged paths. The energy shifts are "never" greater than 10 eV. "never" in my experience. -Hence the answer to your next question. Also, what is your experience as to the actual differences in bonus E0's that you get in ionic compounds? Right now one of my students is working with Sr(NO3)2... should we really expect the difference in bonus E0's between the Sr2+ and the oxygen atoms to be more than 12 eV, or does some kind of charge overlap from the nitrate ions actually make the strontium ions behave as if they are less than +2? [Kelly, Shelly D.] One full electron of ionic bonding gives about 6 eV. So that is about the most you would expect from different ions in a solid. Usually, I have found 3 to 4 eV. You make up most of the valence state change from the shift in the edge position. I have found unrealistic energy shifts when I try to use too much chi(k) data at low k. I'd look there first for you 12 eV shift. HTH Shelly

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RE: [Ifeffit] Using more than one E0
by Kelly, Shelly D. 14 Dec '04

14 Dec '04

Hi Guys, I wanted to add another comment about using multiple E0's. One of the best formulas that I have found involves assigning different atom types different E0's. This method seems to work well for M.S. paths. Here is an example of how it goes. I think that Daniel Haskel was the first to publish this type of E0 stuff. "Single and multiple scattering XAFS in BaZrO3: a comparison between theory and experiment" D. Haskel, B. Ravel, M. Newville and E. A. Stern Physica B 208&209 (1995) 151 Lets pretend that we have a copper oxide that we want to model. First shell Oxygen called O1, Second shell Cu called Cu1, Third shell Oxygen called O2. This method would use three E0's. One for the first shell oxygen atoms, Eo1. One for all the Cu atoms Ecu. and one for all other oxygen atoms Eo2. The Cu-O1 path has E0=Eo1. The Cu-Cu1 path has E0=Ecu. The Cu-O2 path has E0=Eo2. The Cu-O1-Cu-O1 path has E0=Eo1, (only scattering from O1 atom). The Cu-O1-Cu1-Cu path has E0=0.5*Eo1+0.5*Ecu. (scattering once from O1 and once from Cu1) ... And so forth and so on. Now if you set something like this up. You need to look at the results carefully and see if it works. Generally, scattering from an atom that has lost an electron due to an ionic bond will have a positive deltaE, and scattering from an atom that has gained an electron will have a negative deltaE. Of course this negative/positive deltaE is added to the alignment deltaE. If the values for Eo2 and Ecu are the same within the uncertainties of the measurement then you need to make them the same variable, so then you will only have two energy shifts, but you can still use it. This is most often the case as Matt mentioned but I always like to test it out. In addition, one electron transfer is about a shift by 6 eV, so if these values differ by more than say 10 eV something is not right. Since the shift is generally smallish, say 2 eV, your fit has to be really accurate to "see" these shifts. In particular they seem to be most important when you have all the deltaR values constrained in some way so that the error in deltaR is really really small. For example all deltaR values are related to unit cell parameters and atomic positions or and overall expansion term. HTH Shelly -----Original Message----- From: Wojciech Gawelda [mailto:wojciech.gawelda@epfl.ch] Sent: Thursday, May 27, 2004 1:18 PM To: ifeffit(a)millenia.cars.aps.anl.gov Subject: [Ifeffit] Using more than one E0 Hi everybody, I would like to address a couple of questions which are partially related to my recent struggles in fitting some EXAFS data. I'm trying to fit my data using several shells of different neighbors including a few single scattering paths and also so multiple scattering contributions (mainly collinear multiple scattering paths) all calculated with the help of FEFF 8.20. Now, I found once in the FEFFIT manual the following suggestion: one might consider using several different E0's for different paths in order to improve the fit. Ok, the explanation was based on some approximations coming from FEFF code which include incomplete core-hole shielding, lack of angular variations of the valence charge distribution and charge transfer between atoms in polar materials. My question is the following: does anyone of you have some experience with such procedure? And if yes, shall than distinguish between the first shell of nearest neighbors and the rest of the atoms in terms of their E0 corrections (using 2 parameters)? Or perhaps one can use separate E0's for each path? That's one thing... The second question concerns the background correction in Artemis: I was trying to find an easy explanation of what this procedure does during the fit but I guess I'm still somewhat confused...how one can judge whether the spline co-refinement does the right job? Some people on this mailing list underline that one should avoid high correlations between fitting parameters and background parameters in order to make sure that the fit is correct. But is it the only criterion? In some of my fits background line looks kind of constant over the entire R-range which was taken into the fit. Sometimes it becomes like a modulation peaking underneath some scattering paths...even if the background parameters don't correlate significantly with fitting parameters I have my doubts whether the result is trustful. Any hints about this procedure? Well, I'll greatly appreciate any comments and feedback from all you guys. I hope I'll be able to share some of my own soon :-) Cheers, Wojciech ********************************************************************* Wojciech Gawelda Laboratoire de Spectroscopie Ultrarapide (LSU) Institut des Sciences et Ingénierie Chimiques (ISIC), Faculté des Sciences de Base (SB-BSP) Ecole Polytechnique Fédérale de Lausanne (EPFL) CH-1015 Lausanne-Dorigny, Switzerland Tel.: +41 (21) 693 0452 Fax.: +41 (21) 693 0422 E-mail: <mailto:wojciech.gawelda@epfl.ch> wojciech.gawelda(a)epfl.ch WWW: <http://lsu.epfl.ch> http://lsu.epfl.ch *********************************************************************

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