On 07/02/2014 01:06 PM, ZHAN Fei wrote:
Dear all,
when I try to solve my question{*[Ifeffit] path contribution to fit in low R-space position, but the fit bond length is much longer than that*},I find a method from Prof.Calvin to distinguish whether coordination shell is composed by light or heavy element:
http://millenia.cars.aps.anl.gov/pipermail/ifeffit/2007-December/007983.html
A clue can perhaps be obtained by noting the relative height of the peak near 2.3 angstroms compared with the large peak you've fit. As k- weight is raised from 0 to 1 to 2 to 3, the peak at 2.3 angstroms does not grow relative to the first peak. That suggests the scattering may be from another low-Z element like oxygen.
But I still don't know ,why it works.
Hi Zhanfei, First off, I am very pleased to see that you are using the archive of the mailing list as a learning resource. Well done! Lots of questions have been answered here over the years! On this page, http://xafs.org/Tutorials, you will find a link to a document by Matt called "The Fundamentals of XAFS". Look at figure 3.3 on page 15. It's a plot of the back-scattering amplitudes of three different elements. As you can see, they have very different behavior as a function of k. Light things don't scatter very strongly at high k whereas heavy element do. When you change the k-weight, you change how strongly the different regions contribute to the Fourier transform. If you have different elements contributing to the spectrum, then changing the k-weight may give you a way of emphasizing one contribution over another. HTH, B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 Homepage: http://xafs.org/BruceRavel Software: https://github.com/bruceravel