[Wien] XPS is there a shift of fermi energy from core-hole? Can I estimate it?
Peter Blaha
pblaha at theochem.tuwien.ac.at
Mon Apr 13 20:41:48 CEST 2015
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
>>
>>
>> _______________________________________________
>> Wien mailing list
>> Wien at zeus.theochem.tuwien.ac.at
>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>> SEARCH the MAILING-LIST at:
>> http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
>>
>
> --
> -----------------------------------------
> 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
> -----------------------------------------
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> SEARCH the MAILING-LIST at:
> http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
>
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
>
--
-----------------------------------------
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
-----------------------------------------
More information about the Wien
mailing list