[gpaw-users] gpaw-users Digest, Vol 62, Issue 23

[Eric Hermes]

Toma,

I understand that both VASP and GPAW are unable to explicitly create a 
3d 5/2 core-hole state, but I think that's fine as I'm merely attempting 
to calculate shifts in core-level binding energies, rather than absolute 
binding energies.

To touch on the code snippets, would it be possible to create a 
core-hole setup with corehole=(3, 2, 0.5) and run the calculation with 
charge=-0.5? This is what is done in Slater-Janak transition state 
theory, and my understanding from reading the literature is that it is 
more directly comparable to experimental values than the final state 
approximation (which is what you have written).

Also, to respond to your previous email, VASP is capable of including 
spin-orbit coupling through the LSORBIT=.TRUE. flag. I am not sure if 
this is exactly what you were referring to, and I'm not sure it would 
affect my calculations as they have been thus far non-spin-polarized.

Thanks,
Eric

On 3/16/2015 11:45 AM, Toma Susi wrote:
> Hi again,
>
> Ah, if the system is that poorly defined then perhaps you are right. 
> It is also experimentally possible to refer the binding energies to 
> the vacuum level, but in that case you need to measure the sample work 
> function, typically by valence band photoemission (UPS).
>
> Perhaps GPAW would give you some advantage in such a calculation, but 
> the description of a 5d core-hole may be rather poor… You can generate 
> a Pd 3d core-hole setup in your script with:
>
> gen('Pd', name='Pdfch3d', xcname='PBE', corehole=(3, 2, 1.0))
>
> and then apply it to a target atom number # by specifying in the 
> calculator
>
> setups={#:'Pdfch3d’}, # Applying the generated setup to atom number #
> charge=-1 # For a neutral cell
>
> However, this will be neither a 5/2 nor a 3/2 core-hole, but something 
> centro-symmetric and thus not really physical. You might get something 
> sensible for chemical shifts, but I wouldn’t guarantee it.
>
> Although I doubt the error is bigger than what you get from 
> disregarding the spin-orbit coupling, you might get more accurate 
> results by specifying in the core-hole setup generation to add extra 
> projectors to match the GPAW setup for palladium 
> (https://wiki.fysik.dtu.dk/gpaw/setups/Pd.html).
>
> Best,
> Toma
>
>
>> On 16 Mar 2015, at 17:23, gpaw-users-request at listserv.fysik.dtu.dk 
>> <mailto:gpaw-users-request at listserv.fysik.dtu.dk> wrote:
>>
>> Mathias,
>>
>> It sounds to me like GPAW's method for generating the core-hole setup is
>> equivalent to VASP's, so I think their results should be comparable.
>>
>> As far as XPS being taken relative to the Fermi level, I've read that in
>> the literature but I do not think it is actually true, at least for our
>> case. The experimental spectra that I am comparing to are taken for
>> amorphous carbon-supported nanoparticles that are a mixture of metallic
>> Pd, PdOx, and Pd-Te intermetallics, and we are not even certain about
>> the stoichiometry of the intermetallics. Because the system is
>> ill-defined, I don't see how the binding energy could be relative to the
>> Fermi level (because it is not well-defined). In addition, my advisor
>> has spoken to another experimental collaborator for a different project,
>> and he has indicated to us that the XPS spectra they take are with
>> respect to the vacuum energy. I am not at all an expert in this matter,
>> so please correct me if I am wrong.
>>
>> Thanks,
>> Eric
>

-- 
Eric Hermes
J.R. Schmidt Group
Chemistry Department
University of Wisconsin - Madison

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