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Dear Chris,<br>
<br>
I think that the dipole correction is not working in ph.x, but<br>
you could try the new Coulomb cutoff technique implemented<br>
in both pw.x and ph.x by Sohier and coworkers, see<br>
assume_isolated = '2D'<br>
<br>
Regards<br>
<br>
Thomas<br>
<br>
<div class="moz-cite-prefix">On 06.04.2018 15:57, Christoph Wolf
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAMC_G_5zWEUO-u-TzE4iwkO+YQdkfXRHwpJAqBX7xTy+-jE2AA@mail.gmail.com">
<div dir="ltr">Dear all,
<div><br>
</div>
<div>I am curious if someone could shed some light onto the
following:</div>
<div><br>
</div>
<div>I am currently calculating phonons of MgO using QE 6.2.1
and NC PPs from the ONCV library (requirement of
post-processing with YAMBO). Bulk properties (lattice and
vibrational) are very nicely reproduced.</div>
<div><br>
</div>
<div>When moving to slabs (1,2,3 layers with ca 20 A vacuum,
dipfield correction applied) phonons become considerably
"ugly" (very high energy imaginary modes). I was wondering if
there is a "trick" to get better phonons in slabs with polar
surfaces either during ph.x (I tried tighter convergence down
to 10e-16, higher k grids in pw.x, higher q grids in ph.x
without much success) or post-processing (not sure if the
usual ASR are applicable in slabs)?</div>
<div><br>
</div>
<div>Since calculations on the slabs are rather time consuming
any suggestion is very welcome!</div>
<div><br>
</div>
<div>A nice weekend to everyone from San Sebastian,</div>
<div><br>
</div>
<div>Chris <br clear="all">
<div><br>
</div>
-- <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>
</div>
<br>
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<br>
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<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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