On Monday, August 20, 2012 09:53:13 AM Wei Li wrote: > Hi, Bruce, > > Does that mean each shell has a different S02 value?
No. It means that S02 must be evaluated for each path. Or, I suppose, I should say that the product of N and S02 must be evaluated for each path. No! No! Actually, I should say that the product of N and S02 must be evaluated correctly for each path where what I mean by "correctly" depends upon the details of your fitting model. That sounds right! If you are fitting your copper foil data, then "correctly" probably means to let N be the path degeneracy found by the path finder and to use a single S02 parameter for all paths. If you are fitting a crystal with different sites for the absorbing atom -- say the super conductor YBa2Cu3O7, which has 1 Cu atom in the Cu1 site and 2 Cu atoms in the Cu2 site -- then your parameterization of S02 must be scaled accordingly depending on which Feff calculation the path comes from. If you are fitting an amorphous solid or a nanoparticle or something else which unknown coordination, then you are probably best off setting N to 1 and parameterizing S02 for each path in some manner that captures the details of the coordination environment that you are trying to measure. Remember, N and S02 are multiplied together in the EXAFS equation. HTH, B > Wei > > On Mon, Aug 20, 2012 at 9:44 AM, Bruce Ravel <[email protected]> wrote: > > On Monday, August 20, 2012 09:02:28 PM Huaming Guo wrote: > > > I am using the (D)Artemis for EXAFS fitting. However, the "N" is set to > > > > be a > > > > > constant in the (D)Artemis. We can not set the variable for this > > > > parameter. > > > > > How can I do that if I model non crystalline samples using (D)Artemis? > > > Thanks a lot. > > > > In Artemis, N is a pure number, but S02 can take a math expression. > > > > In the EXAFS equation, N and S02 are multiplied together. > > > > Thus, you might consider parameterizing the amplitude by setting N to > > 1 and putting all of the parameterization in the math expression for > > S02. > > > > B > > > > > > -- > > > > Bruce Ravel ------------------------------------ [email protected] > > > > National Institute of Standards and Technology > > Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 > > Building 535A > > Upton NY, 11973 > > > > Homepage: http://xafs.org/BruceRavel > > Software: https://github.com/bruceravel > > > > _______________________________________________ > > Ifeffit mailing list > > [email protected] > > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit -- Bruce Ravel ------------------------------------ [email protected] National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 Homepage: http://xafs.org/BruceRavel Software: https://github.com/bruceravel _______________________________________________ Ifeffit mailing list [email protected] http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
