[Ifeffit] XANES - Peak assignment and ionization potential with
joshua.j.kas at gmail.com
Tue Sep 17 12:45:01 CDT 2013
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.
> What about ionization potential? Does FEFF calculate it, or is there a way to extract it from the spectra?
> On 09/13/13, Bruce Ravel
>> 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.
>> 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
> 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...?
> 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
> End of Ifeffit Digest, Vol 127, Issue 16
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