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
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