[Ifeffit] XANES - relative peak energies

Ross Devol devol at wisc.edu
Tue Sep 17 14:05:41 CDT 2013


Thanks Josh and everyone else for the useful information!
 
Here's another question: How precise should the relative peak energies be compared to experiment? If they don't match up, are there any parameters I can change that might stretch the spectrum or shift peaks relative to one another?

Thanks
Ross 
 
On 09/17/13, Joshua Kas wrote:
> Hi Ross,
> FEFF calculates the Edge energy, as well as the Fermi level. The edge
> energy is accurate to about 1%, which means 1 to 10 eV for most edges
> and systems. Feff also calculates the Fermi level, but does not give a
> good estimate of the ionization potential.
> 
> Also, in reference to your first question, as Bruce suggested, the
> LDOS is a good quantity to look at. If a peak shows up strongly in the
> Ca and the O LDOS, but only weakly in the C LDOS, that is an
> indication that the peak is due to hybridization (bonding) between the
> Ca and O states.
> 
> Cheers,
> Josh
> 
> 
> >
> > What about ionization potential? Does FEFF calculate it, or is there a way to extract it from the spectra?
> >
> > Thanks
> > Ross
> >
> > On 09/13/13, Bruce Ravel
> > wrote:
> >> On 09/13/2013 03:25 PM, Ross Devol wrote:
> >>
> >> >Does anyone know whether FEFF can be used to assign peaks? In other
> >> >words, is there a way to tell which peaks in a calcite O K-edge
> >> >spectrum are due to CO bonds and which to CaO bonds? Also, does
> >> >FEFF calculate the ionization potential and if so, where does it
> >> >output this?
> >>
> >> Feff is a real-space multiple-scattering code. From the RSMS, your
> >> question may not make a lot of sense. The XAS spectrum is a measure
> >> of how the photoelectron interacts with its surroundings. In general,
> >> peaks in the spectrum have something to do with all of the surroundings.
> >>
> >> One way to get a handle, in some sense, on your question is to run
> >> Feff with successively larger values of the FMS parameter. That is,
> >> see what features appear or change in the calculation as you increase
> >> the radius of the cluster considered in the FMS calculation.
> >>
> >> Also of interest will be the partial densities of state as a function
> >> of cluster size. That gives some hints of how Feff sees bonding in
> >> your cluster.
> >>
> >> HTH,
> >> B
> >>
> >>
> >>
> >>
> >> --
> >> Bruce Ravel ------------------------------------ bravel at bnl.gov
> >>
> >> National Institute of Standards and Technology
> >> Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2
> >> Building 535A
> >> Upton NY, 11973
> >>
> >> Homepage: http://xafs.org/BruceRavel
> >> Software: https://github.com/bruceravel
> >> _______________________________________________
> >> Ifeffit mailing list
> >> Ifeffit at millenia.cars.aps.anl.gov
> >> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
> >
> >
> > ------------------------------
> >
> > Message: 2
> > Date: Tue, 17 Sep 2013 11:50:55 -0400
> > From: Bruce Ravel <bravel at bnl.gov>
> > To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> > Subject: Re: [Ifeffit] XANES - Peak assignment and ionization
> > potential with FEFF
> > Message-ID: <52387A5F.8 at bnl.gov>
> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> >
> > On 09/17/2013 01:42 AM, Ross Devol wrote:
> >> What about ionization potential? Does FEFF calculate it, or is there
> >> a way to extract it from the spectra?
> >
> > Are you asking about edge energy on an absolute energy scale? Some
> > measure of that can be found in xmu.dat, but I am not sure what the
> > current state of Feff's ability to calculate that reliably is.
> > Perhaps John, Kevin, or Josh might comment on that...?
> >
> > B
> >
> > --
> > Bruce Ravel ------------------------------------ bravel at bnl.gov
> >
> > National Institute of Standards and Technology
> > Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2
> > Building 535A
> > Upton NY, 11973
> >
> > Homepage: http://xafs.org/BruceRavel
> > Software: https://github.com/bruceravel
> >
> >
> > ------------------------------
> >
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> > Ifeffit at millenia.cars.aps.anl.gov
> > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
> >
> >
> > End of Ifeffit Digest, Vol 127, Issue 16
> > ****************************************
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