[Ifeffit] controlling valence state in FEFF9 XANES sims

Matthew Marcus mamarcus at lbl.gov
Thu Oct 6 23:37:03 CDT 2011

I'm involved in a project involving mixed Fe-Cr oxides.  There's some evidence that the presence of Fe2+ in these oxides causes distinctive features to appear
in the XANES at the Cr K-edge.  I would like to simulate this situation to see if a valence effect could really explain it.  However, FEFF9 doesn't seem to
have an obvious mechanism for controlling the valence of the atoms or even assuring charge neutrality of the cluster.  For instance, as a test, I simulated
goethite (FeO(OH)) with and without the H atoms and got almost the same result, even though charge balance works for FeO(OH) and not for FeO(O<nothing>).
I know that there is the ION card, but it's not clear how to choose the value so as to get a given formal oxidation state or how to determine what charges are
present on any atoms in the cluster.  Any ideas out there?

Also, I find that the XANES is best simulated if I make S02=0.7 or so.  If S02=1, the features are too intense.

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