<html data-lt-installed="true">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body>
<p>It could be just one case of Hartree Fock giving bad results for
metallic systems, i.e. Phys. Rev. B 20, 1504 (1979), in particular
the steep bands imply a vanishing DOS at the Fermi energy. But I'm
not at all an expert of this kind of applications...</p>
<p>cheers<br>
</p>
<div class="moz-cite-prefix">On 21/09/2022 16:54, Lorenzo Sponza
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:de7badd65344b4447545cc652212d8fe@onera.fr">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<p>Hello everybody.</p>
<p>I'm having some troubles in calculating the band structure of
bulk Iridium with HSE06. In order to do that, I'm using the
'fake k-points' method, so I extract the band structure from a
SCF calculation using an home-made post-processing code which is
attached to this email. I run each simulation in a different
folder to be sure not to overwrite important files. I'm using
the marzari-vanderbilt smearing method with degauss values
ranging from 0.011 to 1.0 and regular k-point grids ranging from
2x2x2 to 12x12x12 while the fake k-points list counts 26
k-points in all cases. You can find an example of input file
attached to the email. In parallel I have done also some PBE
calculations with the standard procedure SCF+BANDS.</p>
<p>In the case of the PBE calculation, I don't observe differences
in the band dispersion depending on the degauss value, but the
Fermi level moves up for higher values of degauss and the
k-point convergence is faster. </p>
<p>What I observe in the case of HSE06 is that the dispersion
itself does change depending on the degauss value. Please see
the attached graphs. In particular, for quite "standard" values
of the degauss (0.02), the band structure presents weird jumps
crossing the Fermi level, whereas for high values ( degauss =
0.8 ) the dispersion is smoother across Fermi, converges very
quickly with the regular k-point grid and looks somewhat similar
to the PBE one. I understand it as a consequence of the fact
that hybrids have a certain amount of EXX which act only on
occupied states. Since the occupation is not abrupt in metals
and is modified by the smearing, then the potential changes in a
continuous way as a function of degauss.</p>
<p><br>
</p>
<p>Hence my questions:</p>
<p>- In PBE calculations, how can I know what is the right value
of the degauss parameter? I saw answers in the forum as if it is
a compromise between k-points and smearing amplitude and ideally
an infinitely dense grid would give the exact result with no
smearing. However this answer does not help me in understanding
where is the right Fermi energy because a finer grid does not
solve the issue.</p>
<p>- Are hybrid functionals a safe choice for the calculation of
the electronic structure and band alignment in metals?</p>
<p>- Is there a rule (rigorous or rule of thumb) to set the
degauss value in metals when using hybrid potentials?</p>
<p>- Am I completely wrong, and I'm just making some mistake at
the level of scf or of the band extraction? (I have no
experience on metals and little on hybrids)</p>
<p>Thanks a lot for your help ! </p>
<p><br>
</p>
<div id="v1_rc_sig">-- <br>
<div class="v1pre">Dr. Lorenzo Sponza<br>
Chargé de Recherche au CNRS<br>
Laboratoire d'étude de microstructures (LEM), CNRS-ONERA<br>
29 Avenue de la division Leclerc, 92322 Châtillon<br>
Tel: +33146734464</div>
</div>
<br>
<fieldset class="moz-mime-attachment-header"></fieldset>
<pre class="moz-quote-pre" wrap="">_______________________________________________
The Quantum ESPRESSO community stands by the Ukrainian
people and expresses its concerns about the devastating
effects that the Russian military offensive has on their
country and on the free and peaceful scientific, cultural,
and economic cooperation amongst peoples
_______________________________________________
Quantum ESPRESSO is supported by MaX (<a class="moz-txt-link-abbreviated" href="http://www.max-centre.eu">www.max-centre.eu</a>)
users mailing list <a class="moz-txt-link-abbreviated" href="mailto:users@lists.quantum-espresso.org">users@lists.quantum-espresso.org</a>
<a class="moz-txt-link-freetext" href="https://lists.quantum-espresso.org/mailman/listinfo/users">https://lists.quantum-espresso.org/mailman/listinfo/users</a></pre>
</blockquote>
<div class="moz-signature">-- <br>
<small>Dr. Lorenzo Paulatto<br>
IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université<br>
phone: +33 (0)1 442 79822 / skype: paulatz<br>
<a href="http://www.impmc.upmc.fr/~paulatto/"
class="moz-txt-link-freetext">http://www.impmc.upmc.fr/~paulatto/</a>
- <a href="https://anharmonic.github.io/"
class="moz-txt-link-freetext">https://anharmonic.github.io/</a><br>
23-24/423 B115, 4 place Jussieu 75252 Paris CX 05<small></small></small></div>
</body>
<lt-container></lt-container>
</html>