On Tuesday 30 October 2007 21:21:59 Tai-Yen Chen wrote:
hi, Can anyone tell me whether I can use ifeffit to do this job?
I want to know the % change in chi when the molecule have 3% change in radius? All I have is just the crystal struture of gamma-Fe2O3, which means I can only get the Feff. How can I introduce 3% change in redius so that I can get the difference of chi? Can anyone help me? Tanks a lot.
Hi TaiYen, Since you are asking about using Ifeffit, I presume that you are interested in changes in the EXAFS spectrum rather than the XANES. There are a number of ways you might approach this problem. Probably the best way of doing so would be to do a proper fit to measured data so that you can get a good measure of things like sigma^2 and e0. Then, using the results of the fit, modify the deltaR parameters for each path used in the fit to be 3% larger. Then simply add up the paths using the fitted values for sigma^2, e0, and so on. You can also do something similar without actually doing a fit to data. Use Artemis or ifeffit itself to increase R for each path and simply sum the paths without using fitted values for sigma^2 and so on. The easiest way of doing so would be to set deltaR for each path equal to "0.03*reff". That will expand the length of each path by 3%, thanks to the magic of the special "reff" parameter in Ifeffit. Another way of doing this (and a decent way of doing so for a XANES calculation) would be to use Feff's rmultiplier keyword: http://leonardo.phys.washington.edu/feff/wiki/index.php?title=RMULTIPLIER HTH, B -- Bruce Ravel ----------------------------------- bravel@bnl.gov National Institute of Standards and Technology Building 535A, Room M7 c/o Brookhaven National Laboratory Upton NY, 11973, USA My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/