[Ifeffit] Relatively reduced ionization edge as opposed to oxidized !

Ganesh Subramanian gunkanna at gmail.com
Wed Mar 1 08:47:35 CST 2017


Dear all,

I have been running the FEFF to simulate for XANES spectra for the
cobalamins (Vitamin B12 cofactors). The issue of interest is between three
compounds - Methylcobalamin (Me-Cbl), Cyanocobalamin (CN-Cbl) and
Hydroxocobalamin (OH-Cbl).
Experimentally, Me-Cbl is supposed to the most reduced (in terms of the
energy of onset of the rising absorption edge). OH-Cbl and CN-Cbl are
supposed to be oxidized wrt Me-Cbl. (The official oxidation state of Cobalt
for all the above three systems is +3).
However, the simulations do no reflect this and it consistently seems to
predict a reduced absorption edge for both OH-Cbl and CN-Cbl, in comparison
to Me-Cbl.
I checked the literature to confirm that the molecular coordinates that we
are using as input (obtained after structure optimization using DFT -
Gaussian09) is consistent with prior literature.

I am wondering if there is anything related to FEFF that I miss
understanding, to note why this is occurring. I am attaching the input
files for the three models (these are all truncated to reduce the
computational expense on DFT optimization) and the experimental and FEFF
simulated spectra that I had obtained.

Any help in understanding this seeming discrepancy is much appreciated.

Thanking you,

Ganesh
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