RE the effect of bond length on edges: this physical effect is normal and has been known for many decades. Although the XANES is a composite of mu_zero, single scattering, and multiple scattering, there is an underlying simple effect of bond length. Broad features on K-edges (which are dominated by mu_zero and single scattering) shift approximately as delta E ~ k^2 ~ 1/r^2, where r is the average nearest neighbor bond length, simply from the phase advance in the single scattering component. The phases of the higher frequency oscillations from multiple scattering advance more rapidly when the bond length is increased. L edges are a bit different because there are often bound states near the fermi level that have to be accounted for. I studied this in my thesis quite a while ago (gb thesis 1984) in the pre-FEFF era. Theoretically, by freezing the charge densities of the atoms, changing the bond lengths (and other geometrical parameters), and then calculating the XANES in both single scattering and multiple scattering approximations shows that it is primarily a geometrical effect, for the reason I outlined above. It also is in accord with experiment as I showed with Mn oxides. A basic introduction can be found here: http://gbxafs.iit.edu/training/XANES_intro.pdf grant bunker On Jun 23, 2008, at 9:34 AM, ifeffit-request@millenia.cars.aps.anl.gov wrote:
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Today's Topics:
1. RMULTIPLIER-Card (s440697@stud.uni-goettingen.de)
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Message: 1 Date: Mon, 23 Jun 2008 16:33:50 +0200 (CEST) From: s440697@stud.uni-goettingen.de Subject: [Ifeffit] RMULTIPLIER-Card To: ifeffit@millenia.cars.aps.anl.gov Message-ID: <53054.134.76.41.165.1214231630.squirrel@webmail.stud.uni-goettingen.de
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Hi, I have a question concerning the RMULTIPLIER-Card in XANES- Calculations. I made some calculations with different rmult values (1.00, 1.01, 1.05, 1.10) and found a shift of the absorption-edge or rather the slope of the peak. I attached the diagram of this calculation (Sulfur-K-edge of gypsum).
My question is, what could be a physical reason for this behaviour? With this Parameter one change the interatomic disctances. Hence the interference phenomena and the curve progression should be change, too. Is this right?
Thanks for your help.
Have a nice day, Eckhard
PS: the same behaviour occurs in a inverse sense for rmult < 1
--------------------------------- Eckhard Bosman e.bosman@stud.uni-goettingen.de +49 (0)551-39-14441 Raum: E0.104 Institut f?r R?ntgenphysik Friedrich-Hund-Platz 1 37077 G?ttingen Germany