[Wien] XPS is there a shift of fermi energy from core-hole? Can I estimate it?
David Olmsted
olmsted at berkeley.edu
Mon Apr 13 20:37:18 CEST 2015
Laurence,
Thank you for the suggestion. It makes sense, but it may not work here.
For the 48 atom supercell of AlPO4, excluding the two P atoms that are
second neighbors of the Al with the half core-hole, the difference in the
P-1s energy between the run with and without the half core-hole range from
0.43 eV to 0.55 eV for the various atoms. On the other hand, excluding the
atom with the core-hole, the difference for Al-1s energy between the two
runs varies from -0.02 to 0.12 eV. (The Al-1s is at about -110 Ry, and the
P-1s at about -150 Ry.) So the different deep core levels disagree too
much.
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 Laurence Marks
Sent: Monday, April 13, 2015 9:36 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?
A comment that may be useful. If you have a deep core level on another atom
that is not that close you may be able to use that as a reference instead --
seemed reasonable when I used it in the past for something else.
On Mon, Apr 13, 2015 at 11:04 AM, David Olmsted <olmsted at berkeley.edu>
wrote:
> 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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--
Professor Laurence Marks
Department of Materials Science and Engineering Northwestern University
www.numis.northwestern.edu Corrosion in 4D: MURI4D.numis.northwestern.edu
Co-Editor, Acta Cryst A "Research is to see what everybody else has seen,
and to think what nobody else has thought"
Albert Szent-Gyorgi
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