[Ifeffit] Pre-edge reproduction in FEFF8

[joshua jason kas]

Hi Janine,
I think there could be two issues here,

 	1) The feff fermi level is not highly accurate, so you should set
 	   it using the output of your DFT calculation. This can be done
 	   by setting the vr argument to the EXCHANGE card in feff. Note
            that a positive value of vr shifts the fermi level by -vr.
 	2) A second pre-edge peak shows up if you use a slightly distorted
            geometry, which suggests that vibrational distortion will have
 	   an effect due to symmetry breaking.

Note that the second peak does not appear in the spectrum unless the fermi 
level is shifted down by about an eV, so maybe extra peaks in the other 
systems are getting cut off due to an overestimated fermi level.
Cheers,
Josh Kas

On Wed, 9 Jul 2008, ifeffit-request at millenia.cars.aps.anl.gov wrote:

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>   1. Pre-edge reproduction in FEFF8 for Cobalt molecules
>      (Janine GRATTAGE)
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>
> ----------------------------------------------------------------------
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> Message: 1
> Date: Wed, 09 Jul 2008 15:07:56 +0200
> From: Janine GRATTAGE <janine.grattage at esrf.fr>
> Subject: [Ifeffit] Pre-edge reproduction in FEFF8 for Cobalt molecules
> To: Ifeffit at millenia.cars.aps.anl.gov
> Message-ID: <4874B82C.5040607 at esrf.fr>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Dear all,
>
> I am studying the K edge XANES of a series of cobalt containing
> molecules and I am having trouble reproducing the pre-edge features
> using FEFF8.4. For all three "acac" molecules I studied (which have
> different acetylacetonate ligand arrangements on the Co atom), the
> experimental pre-edges show two or three features of varying
> intensities, but the FEFF calculated pre-edge is identical for each
> molecule. I have tried for one of the molecules, Co(acac)2, to use both
> the dipole contribution only, and both the dipolar and quadrupole
> components in the calculations, by using the card MULTIPOLE 0 and
> MULTIPOLE 2 - two figures are attached.
>
> For the input file (attached also) the atomic coordinates were
> calculated by using a density functional theory minimised molecular
> geometry using ADF. Any suggestions as to how to improve the pre-edges
> (i.e. show more than one feature, and vary for the different molecules)
> would be welcome!
>
> Thank you in advance,
>
> Dr. Janine Grattage
> Postdoc, ESRF.
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