[Ifeffit] FEFF-SCF and Enot in Artemis

[Frommer Jakob]

Dear all!

Recently I read the two inspiring XAFS13-contributions of Shelly and Bruce dealing with the energy-shift (p.132) and the use of SCF-calculations (p. 137). In this respect I have a question regarding the Enot parameter in Artemis: Plotting the mue (4th column in xmu.dat) of a FEFF8.4 SCF calculation (of a transition metal oxide; here: Fe or Cr) against the second column ("e") of xmu.dat, I end up with a fairly decent reconstruction of my experimental XANES: the onset of the pre-edge resonances is located at negative energies (if I am right this is referred to as E_0 (bottom of the conduction band)) and the energy zero (i.e. Fermi energy) is located somewhere in the rising part of the absorption edge. If I then use the same (SCF) potentials and let FEFF do a path-expansion run, the header of the feffnnnn.dat contains a (negative) quantity called "edge", which gives exactly the difference between E_0 and E_fermi (as also explained in Matt's article: J. Sync. Rad., 2001, pp. 96-100). In the xmu.dat, k seems to be calculated relative to E_0 (i.e. to a negative energy in the 2nd ("e") column). Plotting a path in Artemis (or the xmu calculated for a single path) I had the impression that again k is referenced to E_0 (onset of the pre-edge feature) rather than to E_fermi (somewhere in the rising part of the edge). Is this true? Assuming that I set the E0-parameter in Athena to the first inflection point of the main edge (so in the upper nomenclature to something like E_Fermi) and assuming further that I do a shell-fit in Artemis, wouldn't I expect to end up (in an ideal case) with an Enot similar to the quantity "edge" given in the feffnnnn.dat rather than a Enot of (close to) 0?

I also found a mailing-list contribution (dating back to 2004) of Wojciech and Matt addressing a similar topic 
- still it is not clear to me what the effect on Artemis' Enot will be.

I hope I did not confuse too many things. I will greatly appreciate any hint clarifying this situation. 

With many thanks and best regards

Jakob

 
___________________________________________________ 
Jakob Frommer 
Soil Chemistry Group 
Institute of Biogeochemistry and Pollutant Dynamics, 
ETH Zürich 
Universitätstrasse 16, 
CHN F19 
CH - 8092 Zürich 
Tel: +41 44 632 87 58 
Fax: +41 44 633 11 18 
web: http://www.ibp.ethz.ch/research/soilchemistry