February 2020 - Ifeffit - millenia.cars.aps.anl.gov

Re: [Ifeffit] Ifeffit Digest, Vol 169, Issue 9
by Abhinav Prabhakar 05 Aug '20

05 Aug '20

Hello, Thank you for your reply. Attached is the CIF file in question. The crystal is Tobermorite 14A, taken from COD website. However, the structure has partial occupancy and it is modified to include full occupancy. The modified CIF file shows a space group of B11b (and cannot be recognized by Artemis). I tried a C1c1 space group (it works) but it shows the same structural values as a P11b. Regards, AP On Tue, Mar 14, 2017 at 1:00 AM, <ifeffit-request(a)millenia.cars.aps.anl.gov> wrote: > Send Ifeffit mailing list submissions to > ifeffit(a)millenia.cars.aps.anl.gov > > To subscribe or unsubscribe via the World Wide Web, visit > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > or, via email, send a message with subject or body 'help' to > ifeffit-request(a)millenia.cars.aps.anl.gov > > You can reach the person managing the list at > ifeffit-owner(a)millenia.cars.aps.anl.gov > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Ifeffit digest..." > > > Today's Topics: > > 1. Re: Space group type in Artemis (Bruce Ravel) > 2. Data export and coordination number (Abhinav Prabhakar) > 3. Re: Data export and coordination number (Bruce Ravel) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Mon, 13 Mar 2017 09:20:14 -0400 > From: Bruce Ravel <bravel(a)bnl.gov> > To: XAFS Analysis using Ifeffit <ifeffit(a)millenia.cars.aps.anl.gov> > Subject: Re: [Ifeffit] Space group type in Artemis > Message-ID: <3853f1f7-61fd-6886-306f-040c540ecae1(a)bnl.gov> > Content-Type: text/plain; charset=windows-1252; format=flowed > > On 03/11/2017 05:56 AM, Abhinav Prabhakar wrote: > > Hello, > > > > I have a question about the working of Artemis as a new user. > > > > Artemis does not recognize the space group B11b. When importing a cif > > file of a crystal with this symmetry, it sends a prompt message that the > > space group symbol cannot be recognized. As a result, I changed it to > > P11b and it works. But would this change any crystal information (for > > eg. Degen, Reff values) significantly? > > I am not a crystallography expert in any sense. When I wrote Artemis, I > meticulously followed what I found in the fourth edition of the > International Tables for Crystallography, Volume A. Every symbol > defined in there is recognized by Artemis. (Well, I guess I should say > that every symbol is /supposed to be/ recognized by Artemis. If one is > missing, that's a bug and should be reported.) > > "B11b" is not a symbol that I found in my copy of ITC volume A. As > Robert suggested, there may be a way to rotate group 9 so that "B11b" is > an interpretable symbol in the abstract. But Artemis does not know how > to do that. (Nor do I.) > > "P11b" is a setting for space group #7. If, as Robert suggests, your > CIF file is for space group #9, then the answer to your last question is > yes. It is plainly obvious that using a different space group will > change the degeneracies and distances. > > > Of course, you did not bother to include a copy of the CIF file in > question to your original email, so it is not actually possible for > Robert or I or anyone else to actually help you effectively. > > At the risk of sounding like an annoyingly broken record, everyone > should take the time to ask a good question or write an actionable bug > report: > > http://bruceravel.github.io/demeter/documents/SinglePage/help.html > http://bruceravel.github.io/demeter/documents/SinglePage/bugs.html > > B > > > -- > Bruce Ravel ------------------------------------ bravel(a)bnl.gov > > National Institute of Standards and Technology > Synchrotron Science Group at NSLS-II > Building 743, Room 114 > Upton NY, 11973 > > Homepage: http://bruceravel.github.io/home/ > Software: https://github.com/bruceravel > Demeter: http://bruceravel.github.io/demeter/ > > > ------------------------------ > > Message: 2 > Date: Mon, 13 Mar 2017 21:48:31 +0800 > From: Abhinav Prabhakar <abhi.prabhakar(a)gmail.com> > To: ifeffit(a)millenia.cars.aps.anl.gov > Subject: [Ifeffit] Data export and coordination number > Message-ID: > <CA+nbL85FJReunY1Am1oeNTMtFskXMd8FmH_OgaO00mnmew2c-g(a)mail.gmail. > com> > Content-Type: text/plain; charset="utf-8" > > Hello, > > As a new user, I have some questions related to the use of Athena and > Artemis: > > i) Is it possible to extract the normalized/background corrected data from > Athena (in E-,k- and R- space) and export it as numbers (to Excel perhaps)? > > ii) Using Artemis, how can coordination numbers (N) be expressed as 'guess' > parameters (Artemis allows only numerical values for N)? > > Thank you. > > Regards, > > Abhinav Prabhakar (Mr.) >

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Larch 0.9.47
by Matt Newville 18 Apr '20

18 Apr '20

Hi Everyone, Larch 0.9.47 is now available, with installers and source code at https://xraypy.github.io/xraylarch/installation.html. For python users, there is a plain python package available on PyPI and conda packages for Anaconda Python. See the installation docs for more details. There have been several improvements and bug fixes, especially for the XAS Viewer application and for XRF modeling in the nearly six months since the last release. In particular, there have been two improvements to basic XAFS and XANES data processing, both based on user reports and comparisons to older versions of Ifeffit/Athena and give a noticeable change in XAFS and XANES processing. First, the ranges used in by the pre_edge() function for finding the edge step for normalization are now better determined from the actual data range rather than simply being hard-wired numbers. These improvements were long over-due and give noticeably better default results for XANES data, especially for relatively low-energy edges such as S and Cl K edges. When reading Athena Project files (say, to import into XAS Viewer), the pre-edge and normalization ranges from the Athena Project file will be preserved. When reading in new raw data, or if you select the "Use Default Setting" button on the Normalization Panel for any group in XAS Viewer, the newer defaults will be used. You can always alter these values, but in playing around with this with a range of datasets, the new defaults seem to give a noticeable improvement in almost all cases and rarely bad. Second, as a few users have pointed out or gently hinted at over many months, there were sometimes significant differences in the background removals between classic Autobk/Ifeffit/Athena and Larch, with Larch sometimes being noticeably and inexplicably worse. I believe this involved two different problems. One was introduced a while back when implementing an estimate of delta_chi - the variance in chi due to the background subtraction. This estimate is important, but I botched some of the configurations of the number of knots, fit range, and Rbkg. The other problem was that "spline clamps" were just done too differently in Larch and Ifeffit/Athena. I believe this is now working much better: the background results are much more consistent, and do not occasionally get "very bad". They also happen to be generally closer to Autobk/Ifeffit/Athena, and perhaps slightly better because the fit range in R-space is now more consistently determined (instead of wandering +/- a few R data points around Rbkg where the misfit will often be the largest). In addition, `delta_chi` (never calculated in Ifeffit/Athena) is now also more consistent. One consequence of this change is that a very small change in Rbkg (of say 0.01 to 0.05 Ang) may actually give no difference at all in mu0(E) or in chi(k). I bring these changes up because I think they will be noticeable. I think they are both improvements, but let me know if you find cases for which you think are now made worse. Possibly related: one thing that I definitely noticed in going through several example data sets was that I tended to favor a k-weight of 2 instead of 1 for background subtraction -- so much so that it seemed like this might be a better default. I did not change this default yet, but if you have a strong opinion on this, that might be a good topic for discussion here. There are some documentation improvements, but this is an ongoing process and never complete. It is also one area where help and feedback would greatly be appreciated. If you or your students have time to work through the larch examples and/or documentation and make improvements or even suggestions for improvements in readability or completeness, it would be greatly appreciated. Thanks, --Matt Newville

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APS/IIT XAFS Summer School Announcement
by Carlo Segre 21 Feb '20

21 Feb '20

The 2020 APS/IIT Summer XAFS School will be held from July 12-17, 2020 in Chicago. Please see attached document for details and contact Grant Bunker <bunker(a)iit.edu> by email for more information with the subject line "2020 XAFS School". -- Carlo U. Segre -- Duchossois Leadership Professor of Physics Director, Center for Synchrotron Radiation Research and Instrumentation Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre(a)iit.edu http://phys.iit.edu/~segre segre(a)debian.org

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XAFS detection limit
by Christian Wittee Lopes 09 Feb '20

09 Feb '20

Dear all, Recently I was questioned about the EXAFS detection limit when describing different metal species in a bimetallic sample. By checking Pd and Cu K-edges, for example, I found Pd metal nanoparticles and CuO clusters, respectively. But additional techniques tell me I can have copper atoms in intimate contact with the Pd nanoparticles. What would be the minimum amount of these "single atoms" needed to be detected by EXAFS? is there a detection limit or it depends on several parameters? Thanks!!! -- *Christian Wittee Lopes* *Postdoctoral Researcher* Institute of Physics, Universidade Federal do Rio Grande do Sul (UFRGS) Phone: +55 54 992430264

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Re: [Ifeffit] Ifeffit Digest, Vol 204, Issue 1
by Christopher Chantler 07 Feb '20

07 Feb '20

Dear Christian and all I think we do not know yet, as the limits are getting better with improved techniques and error analysis, but it is a really good question. One can discuss limits from transmission versus fluorescence, in mM, in ppm; and separately perhaps in mass or mL or microL; or in e.g. atoms or molecules. I think every beamline has some guidelines, for their implementation. So yes it depends a lot on atomic number, density, need for a particular k range (e.g. XANES, normal XAFS, XERT etc.), beamline flux, and experimental method. Some of these estimates will be in the forthcoming International Tables for Crystallography, and earlier estimates are in earlier treatises. Best wishes, Chris -------------------------------------------------------------------------------------- Christopher Chantler, Professor, FAIP, Fellow American Physical Society Editor-in-Chief, Radiation Physics and Chemistry Chair, International IUCr Commission on XAFS; CIT, CCN IPP, International Radiation Physics Society School of Physics, University of Melbourne Parkville Victoria 3010 Australia +61-3-83445437 FAX +61-3-93474783 chantler(a)unimelb.edu.au<https://owa.unimelb.edu.au/owa/redir.aspx?C=c7BoS0kVVkC1_S95-9x9l5cBu6YTjdA…> chantler(a)me.com<https://owa.unimelb.edu.au/owa/redir.aspx?C=c7BoS0kVVkC1_S95-9x9l5cBu6YTjdA…> http://optics.ph.unimelb.edu.au/~chantler/xrayopt/xrayopt.html<https://owa.unimelb.edu.au/owa/redir.aspx?C=c7BoS0kVVkC1_S95-9x9l5cBu6YTjdA…> http://optics.ph.unimelb.edu.au/~chantler/home.html<https://owa.unimelb.edu.au/owa/redir.aspx?C=c7BoS0kVVkC1_S95-9x9l5cBu6YTjdA…> ________________________________ From: Ifeffit <ifeffit-bounces(a)millenia.cars.aps.anl.gov> on behalf of ifeffit-request(a)millenia.cars.aps.anl.gov <ifeffit-request(a)millenia.cars.aps.anl.gov> Sent: Saturday, 8 February 2020 5:00 AM To: ifeffit(a)millenia.cars.aps.anl.gov <ifeffit(a)millenia.cars.aps.anl.gov> Subject: Ifeffit Digest, Vol 204, Issue 1 Send Ifeffit mailing list submissions to ifeffit(a)millenia.cars.aps.anl.gov To subscribe or unsubscribe via the World Wide Web, visit http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit or, via email, send a message with subject or body 'help' to ifeffit-request(a)millenia.cars.aps.anl.gov You can reach the person managing the list at ifeffit-owner(a)millenia.cars.aps.anl.gov When replying, please edit your Subject line so it is more specific than "Re: Contents of Ifeffit digest..." Today's Topics: 1. XAFS detection limit (Christian Wittee Lopes) ---------------------------------------------------------------------- Message: 1 Date: Thu, 6 Feb 2020 23:39:13 -0300 From: Christian Wittee Lopes <chriswittee(a)gmail.com> To: Ifeffit(a)millenia.cars.aps.anl.gov Subject: [Ifeffit] XAFS detection limit Message-ID: <CAJHLRaEz1SJ8dsA+WySAq4Uc2JR=cHApDQ+yZ+yHguqELU+tOw(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" Dear all, Recently I was questioned about the EXAFS detection limit when describing different metal species in a bimetallic sample. By checking Pd and Cu K-edges, for example, I found Pd metal nanoparticles and CuO clusters, respectively. But additional techniques tell me I can have copper atoms in intimate contact with the Pd nanoparticles. What would be the minimum amount of these "single atoms" needed to be detected by EXAFS? is there a detection limit or it depends on several parameters? Thanks!!! -- *Christian Wittee Lopes* *Postdoctoral Researcher* Institute of Physics, Universidade Federal do Rio Grande do Sul (UFRGS) Phone: +55 54 992430264

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