Re: [Ifeffit] Pre-edge reproduction in FEFF8

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@millenia.cars.aps.anl.gov wrote:

Send Ifeffit mailing list submissions to ifeffit@millenia.cars.aps.anl.gov

To subscribe or unsubscribe via the World Wide Web, visit http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit or, via email, send a message with subject or body 'help' to ifeffit-request@millenia.cars.aps.anl.gov

You can reach the person managing the list at ifeffit-owner@millenia.cars.aps.anl.gov

When replying, please edit your Subject line so it is more specific than "Re: Contents of Ifeffit digest..."

Today's Topics:

1. Pre-edge reproduction in FEFF8 for Cobalt molecules (Janine GRATTAGE)

----------------------------------------------------------------------

Message: 1 Date: Wed, 09 Jul 2008 15:07:56 +0200 From: Janine GRATTAGE Subject: [Ifeffit] Pre-edge reproduction in FEFF8 for Cobalt molecules To: Ifeffit@millenia.cars.aps.anl.gov Message-ID: <4874B82C.5040607@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.