[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Charge disproportionation and XANES in FEFF
Hi all,
I am currently working on analyzing spectra from a material which
the creators believe undergo charge disproportionation at a certain
temperature; i. e. they believe Fe4+ --> Fe3+ + Fe5+. I am hoping to
use FEFF8 to give me a qualitative feel for the kinds of changes
that could be expected in the XANES spectrum if this occurs, but I
am not sure how to do this.
The documentation for FEFF warns against using the ION card with the
SCF card, since the SCF calculation will just redistribute the
charge anyway. This makes sense, so I thought I'd try the
calculation without the SCF card, even though I know that will
reduce the accuracy of the simulation dramatically--after all, I'm
just after some qualitative features. For the first calculation, I
tried the case where all Fe was 4+, and arbitrarily divided all
formal valence states by 10 for purposes of the ion card.
When I try it, however, FEFF gives me an error. I'm using FEFF
8.20x8, and have attached the FEFF.INP file and the output.
Most of my experience is in EXAFS, not XANES, so I really haven't
tried anything like this before. I guess I have three questions:
1) How does one simulate charge disproportionation with FEFF?
I will suggest to look at the charge transfert obtained after running
the scf loop or from the ldos.
2) Do XANES calculations without the SCF card have even qualitative
validity, or are they completely pointless?
In principle it is less accurate, especially for the Fermi energy
determination. But it has some validity as feff7 has when using the
xanes card.
3) Why am I getting an error?
It seems that your control card is missing 2 arguments (it needs 6
for feff8, 4 for feff7)
I look forward to reading the responses...
--Scott Calvin
Code 6344
Naval Research Lab
Attachment converted: Einstein:FEFF.INP (TEXT/ttxt) (0007E4A5)
Attachment converted: Einstein:Output.txt (TEXT/ttxt) (0007E4A6)
--
__________________________________________
Michel Jaouen
Universite de Poitiers - UFR Sciences - SP2MI
LMP UMR 6630-CNRS
Boulevard Pierre et Marie Curie - Teleport 2
BP 30179
86962 Futuroscope - Chasseneuil Cedex
France
Tel : (33) 5 49 49 67 37
Fax : (33) 5 49 49 66 92
e-mail : Michel.Jaouen@univ-poitiers.fr
__________________________________________