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Dear Chris,<br>
<br>
in the end it (of course) doesn't (and shouldn't) matter where you
center what.<br>
You can also center the system at z=0 and the dipole at z=0.5. Just
take care<br>
that the distance between system and dipole is large enough.<br>
<br>
Regards<br>
<br>
Thomas<br>
<br>
<div class="moz-cite-prefix">On 27.04.2018 12:06, Christoph Wolf
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAMC_G_7QHx4dOjzFWf7XEje_uMMz=DY_9R8TU1b8dhFn3QaJpg@mail.gmail.com">
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<div>Dear Thomas,<br>
<br>
</div>
thank you for your detailed reply!<br>
<br>
</div>
If I understood this correctly, the ideal situation
would be to have the slab in the center of the cell<br>
</div>
<div><br>
</div>
Atom xx yy 0.5<br>
<br>
(in crystal coordinates)<br>
<br>
</div>
<div>to center the dipole at 0% (=100% due to PBC) a
reasonable choice would be emaxpos=0.95 and
eopreg=0.10. In the dipole example they located the
atoms around z=0 of the cells and put the dipole close
to the center of the cell.<br>
<br>
</div>
<div>Muchas Gracias/Vielen Dank from Spain,<br>
<br>
</div>
<div>Christoph <br>
</div>
<div><br>
<br>
<br>
</div>
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<div class="gmail_extra"><br>
<div class="gmail_quote">On Fri, Apr 27, 2018 at 10:59 AM,
Thomas Brumme <span dir="ltr"><<a
href="mailto:thomas.brumme@uni-leipzig.de" target="_blank"
moz-do-not-send="true">thomas.brumme@uni-leipzig.de</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000"> Dear Chris,<br>
<br>
both planes of the dipole (the one at emaxpos and the one
with the<br>
opposite charge at emaxpos+eopreg) have to be in the
vacuum region.<br>
In fact, there should be enough space such that the
wavefunctions are<br>
essentially zero at the dipole planes. However, if the
dipole is too large,<br>
charge can spill into the vacuum region as plane waves are
not localized<br>
on the system and the charge could be in a lower energy
state at the<br>
dipole. In other words. don't use 50 Angstrom of vacuum as
this will lead<br>
to a very low minimum in the total potential at the
dipole.<br>
See also this paper:<br>
<br>
<a class="m_1612549424893121108moz-txt-link-freetext"
href="https://journals.aps.org/prb/abstract/10.1103/PhysRevB.85.045121"
target="_blank" moz-do-not-send="true">https://journals.aps.org/prb/<wbr>abstract/10.1103/PhysRevB.85.<wbr>045121</a><br>
<br>
In this paper charged systems are discussed but similar
things apply to<br>
the dipole correction. Thus, if your system is centered at
50% of the<br>
cell, center the dipole at zero and converge things with
increasing the<br>
size along z.<br>
<br>
Regards<br>
<br>
Thomas
<div>
<div class="h5"><br>
<br>
<div class="m_1612549424893121108moz-cite-prefix">On
26.04.2018 14:00, Christoph Wolf wrote:<br>
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<div>
<div>Dear all,<br>
<br>
</div>
After trying for a few days I am still
a bit puzzled by the "proper
application" of the dipole correction.
To test this I have made a sheet of
graphene added hydrogen below and
fluorine above. I then apply the
following corrections:<br>
<br>
tefield = .true.<br>
dipfield =.true.<br>
<br>
</div>
and<br>
<br>
eamp = 0.00<br>
edir = 3<br>
emaxpos = 0.80 !(=16 Angstrom)<br>
eopreg = 0.10 ! (=2 Angstrom)<br>
<br>
</div>
The cell is 20 A in total. As I shift the
layer from 0% of the cell to 50% cell
(whilst keeping above emaxpos at 80% and
eopreg at 10% of the cell) the Fermi level
shifts slightly (~0.2-0.5 eV difference)
and the electrostatic potential (pp.x plot
num 11 and then planar average using
average.x as in the work-function example)
is only "flat" in the vacuum region when
the sample is about 3A from the bottom of
the cell (i.e. the z coordinate of atoms
has to be larger than 3 A).<br>
<br>
</div>
Reading the pw.x input I was under the
impression that only emaxpos has to fall
into the vacuum but is there also a "rule of
thumb" for eopreg?<br>
<br>
</div>
Thanks in advance for your help!<br>
<br>
</div>
Best,<br>
</div>
Chris <br clear="all">
<div>
<div>
<div>
<div>
<div>
<div>
<div>
<div><br>
<br>
</div>
<div>PS: I saw the related
discussion, but it does not really
answer this I think... <a
href="http://qe-forge.org/pipermail/pw_forum/2009-December/089951.html"
target="_blank"
moz-do-not-send="true">http://qe-forge.org/pipermail/<wbr>pw_forum/2009-December/089951.<wbr>html</a><br>
</div>
<div>-- <br>
<div
class="m_1612549424893121108gmail_signature">
<div dir="ltr">Postdoctoral
Researcher<br>
Center for Quantum
Nanoscience, Institute for
Basic Science<br>
Ewha Womans University, Seoul,
South Korea</div>
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<span class="HOEnZb"><font color="#888888"> </font></span></blockquote>
<span class="HOEnZb"><font color="#888888"> <br>
<pre class="m_1612549424893121108moz-signature" cols="72">--
Dr. rer. nat. Thomas Brumme
Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry
Leipzig University
Phillipp-Rosenthal-Strasse 31
04103 Leipzig
Tel: +49 (0)341 97 36456
email: <a class="m_1612549424893121108moz-txt-link-abbreviated" href="mailto:thomas.brumme@uni-leipzig.de" target="_blank" moz-do-not-send="true">thomas.brumme@uni-leipzig.de</a>
</pre>
</font></span></div>
</blockquote>
</div>
<br>
<br clear="all">
<br>
-- <br>
<div class="gmail_signature" data-smartmail="gmail_signature">
<div dir="ltr">Postdoctoral Researcher<br>
Center for Quantum Nanoscience, Institute for Basic Science<br>
Ewha Womans University, Seoul, South Korea</div>
</div>
</div>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Dr. rer. nat. Thomas Brumme
Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry
Leipzig University
Phillipp-Rosenthal-Strasse 31
04103 Leipzig
Tel: +49 (0)341 97 36456
email: <a class="moz-txt-link-abbreviated" href="mailto:thomas.brumme@uni-leipzig.de">thomas.brumme@uni-leipzig.de</a>
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