Ok, that makes things much more clear. Thankfully my group has the book, ill be taking a look at that. Thank you for the quick and clear responce.
Much Obliged Mikhail Solovyev On Thu, Jan 19, 2017 at 1:00 PM, <ifeffit-requ...@millenia.cars.aps.anl.gov> wrote: > Send Ifeffit mailing list submissions to > ifeffit@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-requ...@millenia.cars.aps.anl.gov > > You can reach the person managing the list at > ifeffit-ow...@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. delR and sigma2 models for multiple Scattering Paths > (Mikhail Solovyev) > 2. Re: delR and sigma2 models for multiple Scattering Paths > (Bruce Ravel) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Wed, 18 Jan 2017 13:27:29 -0500 > From: Mikhail Solovyev <sarso...@gmail.com> > To: ifeffit@millenia.cars.aps.anl.gov > Subject: [Ifeffit] delR and sigma2 models for multiple Scattering > Paths > Message-ID: > <CABVdVPzfO9KQ_oSkki4cN3RspBfD9+2Gh7Bf0wdS5soT1-J_jw@mail. > gmail.com> > Content-Type: text/plain; charset="utf-8" > > Hello to all. > I'm currently trying to Artemis fit a molecule that is highly symmetric > with multiple scattering paths playing a large role. > delR and sigma2 have been handled rather well for all of the single paths. > I am, however, confused as to how to handle it for multiple scattering > paths. > Reff for them seems to be close to the value of the furthest atom, but is > always ~5-10% off. (which would be my second question, how is Reff > determined for multiple scattering paths) > I've looked at the presentation and examples, such as FeS2. > I am trying to incorporate all of the same variables used in single > scattering paths for multiple scattering paths the best i can. > > Thank you ahead of time. > > Mikhail Solovyev > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: <http://millenia.cars.aps.anl.gov/pipermail/ifeffit/ > attachments/20170118/814df56f/attachment-0001.html> > > ------------------------------ > > Message: 2 > Date: Wed, 18 Jan 2017 13:47:19 -0500 > From: Bruce Ravel <bra...@bnl.gov> > To: XAFS Analysis using Ifeffit <ifeffit@millenia.cars.aps.anl.gov> > Subject: Re: [Ifeffit] delR and sigma2 models for multiple Scattering > Paths > Message-ID: <89ff75ad-447d-6e47-26b9-7a774c104...@bnl.gov> > Content-Type: text/plain; charset=windows-1252; format=flowed > > On 01/18/2017 01:27 PM, Mikhail Solovyev wrote: > > I'm currently trying to Artemis fit a molecule that is highly symmetric > > with multiple scattering paths playing a large role. > > delR and sigma2 have been handled rather well for all of the single > paths. > > I am, however, confused as to how to handle it for multiple scattering > > paths. > > Reff for them seems to be close to the value of the furthest atom, but > > is always ~5-10% off. (which would be my second question, how is Reff > > determined for multiple scattering paths) > > I've looked at the presentation and examples, such as FeS2. > > I am trying to incorporate all of the same variables used in single > > scattering paths for multiple scattering paths the best i can. > > Mikhail, > > The definition of Reff is /always/ "half-path-length". > > For a single scattering path, this is trivial. It's simply the > inter-atomic distance. > > For a multiple scattering path, you add up the length of each leg, then > divide by 2. For the case of strictly collinear multiple scattering > path, Reff is the distance between the two atoms farthest apart. > However, if there are scattering angle that are something other than 0 > or 180 degrees, Reff will be related to interatomic distances via some > kind of trigonometric relationship that has to do with scattering angles. > > You are wise to try to build constraints between SS and MS paths in your > fit. For DeltaR parameters, trigonometry helps, but may only be an > approximation. Possibly a good approximation, but an approximation > nonetheless. > > > Scott discusses how to parameterize sigma^2 in his book: > > https://www.amazon.com/XAFS-Everyone-Scott-Calvin/dp/1439878633 > > There are some situations (see https://doi.org/10.1103/PhysRevB.54.156) > where MS sigma^2 can be related exactly to SS. In general, though, MS > sigma^2s usually can only be approximated by constraint with the SS > sigma^2s. > > https://speakerdeck.com/bruceravel/discussion-of-the- > fes2-exafs-analysis-example?slide=6 > > HTH, > B > > > -- > Bruce Ravel ------------------------------------ bra...@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/ > > > ------------------------------ > > Subject: Digest Footer > > _______________________________________________ > Ifeffit mailing list > Ifeffit@millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit > > > ------------------------------ > > End of Ifeffit Digest, Vol 167, Issue 21 > **************************************** >
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