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Dear Chris,<br>
<br>
one more thing: all these options are just a first approximation.
Looking at the<br>
STMpw tool you cited you'll see that there are more advanced option.<br>
One step further would be including the STM tip, next could be the
wave function<br>
matching ("Bardeen" in that tool), next would be calculating the
zero bias<br>
conductance via the Landauer-Buttiker formula, e.g., with<br>
PWCOND:
<a class="moz-txt-link-freetext" href="http://iramis.cea.fr/Pisp/alexander.smogunov/PWCOND/pwcond.html">http://iramis.cea.fr/Pisp/alexander.smogunov/PWCOND/pwcond.html</a><br>
or WanT: <a class="moz-txt-link-freetext" href="http://www.wannier-transport.org/wiki/index.php/Main_Page">http://www.wannier-transport.org/wiki/index.php/Main_Page</a><br>
and, last but not least, calculating the conductance including a
real bias voltage.<br>
The last option (I think) is not available in QE - there was a code
called Smeagol<br>
which is interfaced with Siesta
(<a class="moz-txt-link-freetext" href="https://www.tcd.ie/Physics/Smeagol/index.html">https://www.tcd.ie/Physics/Smeagol/index.html</a>)<br>
but I don't know if this still works or if it is now included in
Transiesta.<br>
<br>
Cheers<br>
<br>
Thomas<br>
<br>
<div class="moz-cite-prefix">On 1/7/20 3:03 AM, Christoph Wolf
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAMC_G_4s7=UfmTKeXGoG8q9meR1wp9UceBAPT6nrM=y5OP04XQ@mail.gmail.com">
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<div dir="ltr">Dear Thomas,
<div><br>
</div>
<div>thank you very much for your detailed explanation, I will
try and see how far I can get with plot_num 3,7 and 10. A lot
more options here than expected ;)</div>
<div><br>
</div>
<div>Thanks again and with best regards,</div>
<div>Chris </div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sun, 5 Jan 2020 at 06:07,
Dr. Thomas Brumme <<a
href="mailto:thomas.brumme@uni-leipzig.de"
moz-do-not-send="true">thomas.brumme@uni-leipzig.de</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Dear
Chris,<br>
<br>
within the Tersoff-Hamann approximation the STM image is
proportional<br>
to the integral of the local density of states integrated from
the<br>
Fermi energy till the bias voltage:<br>
<br>
<a
href="https://journals.aps.org/prb/abstract/10.1103/PhysRevB.31.805"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://journals.aps.org/prb/abstract/10.1103/PhysRevB.31.805</a><br>
<br>
As far as I remember, the method implemented in PWscf uses
this<br>
approximation. Accordingly, the STS - which is just dI/dV -
should be<br>
proportional to the local density of states at the bias
voltage.<br>
Two things to remember here:<br>
<br>
- STM tips can have apex atoms which have d orbitals and then
Tersoff<br>
Hamann breaks down<br>
- unoccupied states are - from my experience - hardly ever at
the<br>
correct bias compared to experiments. This is due to the
band-gap<br>
problem but also the curvature (effective mass) can be wrong.
Or the<br>
Fermi energy is at a different position in the experiments.
Thus,<br>
depending on the exchange-correlation functional, agreement
for states<br>
in the unoccupied regime could be false positives...<br>
<br>
So, for STM pictures, use the option 5 in pp.x. For STS,
either plot<br>
the closest eigenfunction in real space (option 7) or directly
use<br>
option 3 to plot the local density of states. OR integrate the
LDOS<br>
over a certain region at the specified bias - "simulating" an<br>
experimental broadening... Option 10.<br>
<br>
Hope that helps! Kind regards<br>
<br>
Thomas<br>
<br>
<br>
P.S.: Numerical derivative of the STM pictures should also
work and<br>
I also used this about 10 years ago during my Diploma :)<br>
<br>
<br>
Zitat von Christoph Wolf <a class="moz-txt-link-rfc2396E" href="mailto:wolf.christoph@qns.science"><wolf.christoph@qns.science></a>:<br>
<br>
> Dear all,<br>
><br>
> I was wondering if there is a tool that is able to
calculate the dI/dV for<br>
> output from PWSCF? I guess the way it is currently
implemented would be to<br>
> calculate a set of STM images for different biases and
then take the<br>
> numerical derivative but for larger systems this is
actually really time<br>
> consuming and since we have the wave functions at the end
of a calculation<br>
> there might be a better way to do this. There is for
example this code:<br>
> <a href="https://github.com/qphensurf/STMpw"
rel="noreferrer" target="_blank" moz-do-not-send="true">https://github.com/qphensurf/STMpw</a>
which unfortunately is currently not<br>
> interfaced with PWSCF.<br>
><br>
> Any help is much appreciated!<br>
><br>
> Happy new year everyone!<br>
><br>
> Chris<br>
><br>
> --<br>
> Postdoctoral Researcher<br>
> Center for Quantum Nanoscience, Institute for Basic
Science<br>
> Ewha Womans University, Seoul, South Korea<br>
<br>
<br>
--<br>
Dr. rer. nat. Thomas Brumme<br>
Wilhelm-Ostwald-Institute for Physical and Theoretical
Chemistry<br>
Leipzig University<br>
Phillipp-Rosenthal-Strasse 31<br>
04103 Leipzig<br>
Tel: +49 (0)341 97 36456<br>
email: <a href="mailto:thomas.brumme@uni-leipzig.de"
target="_blank" moz-do-not-send="true">thomas.brumme@uni-leipzig.de</a><br>
<br>
</blockquote>
</div>
<br clear="all">
<div><br>
</div>
-- <br>
<div dir="ltr" class="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>
</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>
</pre>
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