[Ifeffit] XANES - Peak assignment and ionization potential with

[Joshua Kas]

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
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>
>
> ------------------------------
>
> 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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> End of Ifeffit Digest, Vol 127, Issue 16
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