[Wien] XPS is there a shift of fermi energy from core-hole? Can I estimate it?
David Olmsted
olmsted at berkeley.edu
Tue Apr 14 20:15:54 CEST 2015
Peter,
Thank you for the suggestion. It does look like I can make an estimate
this way, at least as to order of magnitude. The offset in where the DOS
goes to zero in relation to the Fermi energy does seem to be small. Of the
order of 0.01 eV.
Best,
David
-----Original Message-----
From: wien-bounces at zeus.theochem.tuwien.ac.at
[mailto:wien-bounces at zeus.theochem.tuwien.ac.at] On Behalf Of Peter Blaha
Sent: Monday, April 13, 2015 11:42 AM
To: A Mailing list for WIEN2k users
Subject: Re: [Wien] XPS is there a shift of fermi energy from core-hole? Can
I estimate it?
Did you ever plot a DOS for the regular structure and the core-hole
supercell ??
I assume, the material is an insulator, so EF should be at the top of the
valence band, just below the "gap".
In the core-hole calculation you get of course a "metal", and EF is NOT at
the top of the valence band, but a bit lower. From the printed EF and the
"band-ranges"
printed in case.scf(2) you can see how much these two numbers differ and in
fact, for a "big" supercell, this difference should go to zero.
I would expect that this E-difference is small anyway, but eventually you
can take the 2p-energy (with core-hole) with respect to the "valence-band
maximum"
(of a undoped case).
Am 13.04.2015 um 18:04 schrieb David Olmsted:
> Dear Peter and all list members,
> [Peter, thanks again for the response below.]
>
> I am modeling XPS binding energy using a one-half core-hole, offset
> by background charge.
> I am looking at the Al-2p states in the Al-P-O-H system, and looking
> at shifts in the XPS energy between hydrated and non-hydrated
> structures. This is for comparison with experimental work.
>
> Is there a shift in the Fermi energy because of the missing 1/2
electron?
> (I believe Laurence Marks made a general mention of worrying about
> Fermi energy shifts when doing XPS in this mailing list.) Since I
> have a finite sized computational cell, it seems like reducing the
> number of electrons should reduce the Fermi energy a bit, compared to
> a larger cell. Is this is so, is there some way I can estimate it,
> either just to see if it is significant, or perhaps even to correct for
it?
>
> Apparently I cannot compare the Fermi energy of different runs,
> each with one-half of a core-hole but different numbers of atoms,
> because of the issue of the zero of energy that Peter Blaha points out
below.
>
> Thanks,
> David
>
> David Olmsted
> Assistant Research Engineer
> Materials Science and Engineering
> 210 Hearst Memorial Mining Building
> University of California
> Berkeley, CA 94720-1760
>
> -----Original Message-----
> From: wien-bounces at zeus.theochem.tuwien.ac.at
> [mailto:wien-bounces at zeus.theochem.tuwien.ac.at] On Behalf Of Peter
> Blaha
> Sent: Friday, April 10, 2015 1:24 PM
> To: A Mailing list for WIEN2k users
> Subject: Re: [Wien] Which fermi energy for XPS?
>
> No, I don't think so.
>
> Every calculation uses its own Energy-zero (the average of the
> Coulomb-potential in the interstitial region is set to zero), so
> clearly one must use EF and E-2p from the same (half-core hole)
calculation.
>
> Eventually, you can check the k-mesh, as with a small k-mesh, EF could
> vary a bit.
> (I hope you have used "comparable k-meshes". This means the mesh for
> the
> 2x2x1 supercell should be by by a factor of two smaller in x,y than
> for the primitive cell
> (eg. 2x2x2 vs 4x4x2)
>
> Am 10.04.2015 um 19:33 schrieb David Olmsted:
>> I am modeling XPS binding energy using a half core-hole, offset by
>> background charge. As I understand the method that has been
>> explained here recently, one computes the binding energy as the
>> energy of the state from case.scfc minus the Fermi energy from ':FER' in
case.scf.
>> Should the Fermi energy be for the configuration with the half
>> core-hole, or a configuration without the core-hole? As explained
>> below, from my results it looks as if it should be the same
>> configuration,
> but without the core hole.
>>
>> Some details:
>> Version 14.2
>> I am computing the differences in the XPS binding energy for Al-2p
>> for cyrstals in the Al-P-O-H system to see how the binding energy
>> changes between hydrated and non-hydrated configurations. This is
>> for comparison with experimental results. (The actual material is
>> amorphous, but I am hoping the effects of on the spectra will be at
>> least qualitatively
>> similar.)
>>
>> The simplest structure is AlPO4, berlinite. I have run two
>> configurations, the primitive cell with 18 atoms, including 3 Al
>> atoms, and a 2x2x1 supercell. In each case I have made one Al
>> unique, then added one-half core-hole in case.inc and offset it with
>> -0.5
> background charge in case.inm.
>> For simplicity I will show the results just for the triplet state.
>> Lines are from case.scf and case.scfc.
>>
>> -------- 2x2x1 supercell, no core-hole
>> :LABEL4: using the command: run_lapw -ec 0.00001 -p <skip>
>> :FER : F E R M I - ENERGY(TETRAH.M.)= 0.0547409802
>> :NEC01: NUCLEAR AND ELECTRONIC CHARGE 720.00000 720.00112
>> :NEC02: NUCLEAR AND ELECTRONIC CHARGE 720.00000 720.00000
>> :NEC03: NUCLEAR AND ELECTRONIC CHARGE 720.00000 720.00000
>>
>> -------- primitive cell, no core-hole
>> :LABEL4: using the command: run_lapw -ec 0.00001 -p -NI <skip>
>> :FER : F E R M I - ENERGY(TETRAH.M.)= 0.0564539224
>> :NEC01: NUCLEAR AND ELECTRONIC CHARGE 180.00000 180.00073
>> :NEC02: NUCLEAR AND ELECTRONIC CHARGE 180.00000 180.00000
>> :NEC03: NUCLEAR AND ELECTRONIC CHARGE 180.00000 180.00000
>>
>> -------- 2x2x1 supercell, half core-hole
>> :LABEL4: using the command: run_lapw -ec 0.00001 -p <skip>
>> :WARN : CHARGED CELL with -0.500
>> :FER : F E R M I - ENERGY(TETRAH.M.)= 0.0609755546
>> :NEC01: NUCLEAR AND ELECTRONIC CHARGE 719.50000 719.50115
>> :NEC02: NUCLEAR AND ELECTRONIC CHARGE 719.50000 719.50000
>> :NEC03: NUCLEAR AND ELECTRONIC CHARGE 719.50000 719.50000
>> <case.scfc>
>> :2P 001: 2P -5.274530454 Ry
>>
>> ------- primitive cell, half core-hole
>> :LABEL4: using the command: run_lapw -ec 0.00001 -p -NI
>> :WARN : CHARGED CELL with -0.500
>> :FER : F E R M I - ENERGY(TETRAH.M.)= 0.0944258517
>> :NEC01: NUCLEAR AND ELECTRONIC CHARGE 179.50000 179.50067
>> :NEC02: NUCLEAR AND ELECTRONIC CHARGE 179.50000 179.50000
>> :NEC03: NUCLEAR AND ELECTRONIC CHARGE 179.50000 179.50000
>> <case.scfc>
>> :2P 001: 2P -5.268297265 Ry
>>
>> --------------
>>
>> The energy of the state differs by 6 mRy (85 meV) between the
>> supercell and the primitive cell, making me hopeful that the
>> supercell is reasonably converged as to size. The Fermi energy,
>> though differs by 40 mRy (540 meV), so probably the supercell is not
>> converged with respect to size for the Fermi energy. In the limit of
>> a large supercell, it would seem that the Fermi energy should
>> converge to the Fermi energy for the configuration without the core
>> hole. So it seems to me that I should use the Fermi energy from the
>> configuration without the core-hole and compute the binding energy as
>> -5.2745 - 0.0547 =
> -5.329 Ry. Is this correct?
>>
>> Thanks,
>> David
>>
>> David Olmsted
>> Assistant Research Engineer
>> Materials Science and Engineering
>> 210 Hearst Memorial Mining Building
>> University of California
>> Berkeley, CA 94720-1760
>>
>>
>> _______________________________________________
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>> l
>>
>
> --
> -----------------------------------------
> Peter Blaha
> Inst. Materials Chemistry, TU Vienna
> Getreidemarkt 9, A-1060 Vienna, Austria
> Tel: +43-1-5880115671
> Fax: +43-1-5880115698
> email: pblaha at theochem.tuwien.ac.at
> -----------------------------------------
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--
-----------------------------------------
Peter Blaha
Inst. Materials Chemistry, TU Vienna
Getreidemarkt 9, A-1060 Vienna, Austria
Tel: +43-1-5880115671
Fax: +43-1-5880115698
email: pblaha at theochem.tuwien.ac.at
-----------------------------------------
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