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-boun...@zeus.theochem.tuwien.ac.at
[mailto:wien-boun...@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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--
-----------------------------------------
Peter Blaha
Inst. Materials Chemistry, TU Vienna
Getreidemarkt 9, A-1060 Vienna, Austria
Tel: +43-1-5880115671
Fax: +43-1-5880115698
email: pbl...@theochem.tuwien.ac.at
-----------------------------------------
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_______________________________________________
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SEARCH the MAILING-LIST 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: pbl...@theochem.tuwien.ac.at
-----------------------------------------
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