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<div class="moz-cite-prefix">Hi <br>
<br>
Have you tried to increase the k_point mesh ? 4 4 4 seems a
little bit lax as mesh for MAPbI3. <br>
If I remember well I am afraid that to get convergence you will
need something like 10X10X10.<br>
As for the structure neighboring methylammoniums like to orient
differently one from the other, you should probably use a larger
cell. Also consider to add some correction for van der Waals
interactions see here (
<a class="moz-txt-link-freetext" href="https://www.quantum-espresso.org/Doc/INPUT_PW.html#idm45922794348896">https://www.quantum-espresso.org/Doc/INPUT_PW.html#idm45922794348896</a>)<br>
<br>
hope it helps <br>
Pietro <br>
<br>
<br>
On 02/21/2019 04:17 AM, Julien Barbaud wrote:<br>
</div>
<blockquote type="cite"
cite="mid:a55d199b-54b2-09be-4cc5-9826e0151a09@sjtu.edu.cn">
<meta http-equiv="content-type" content="text/html; charset=utf-8">
Dear users,
<div class="moz-forward-container">
<div class="moz-forward-container">
<p><br>
</p>
<p>I am new to QE, and trying to run a simple scf calculation
on a CH3NH3PbI3 crystal (semi-conducting material). I am
using ultrasoft pseudopotentials based on the
exchange-correlation functionnal PBEsol.<br>
</p>
<p> I set up a first input, with values of parameters inspired
from literature on the subject. However, I could not reach
convergence after 100 iterations. The estimated error was
actually "exploding" to very high values, indicating a
serious problem. I tried several changes but was
unsuccessful: <br>
</p>
<ul>
<li> varying plane-wave cutoff energy does not solve the
problem (cf attached ecut.png, giving the estimated error
as a function of the number of iterations. It is shown
here only on the first 15 iterations as the results pretty
much only stall from there)</li>
<li> varying cutoff energy for charge (cf ecutrho.png)</li>
<li>taking larger k-point sampling (not shown)</li>
<li> I also read that for metallic or "close to metallic
conductors", there might be problems with the first
unoccupied states that can be solved by adding a few empty
bands. My system being a semi-conductor, I tried adding
additional bands using a m-p smearing but no improvement
was found (not shown)</li>
</ul>
<p><br>
</p>
<p>The only change that I found effective was to reduce the
mixing_beta factor.<br>
</p>
<p><br>
</p>
<p>It effectively prevents the error from diverging to very
large values, but I still do not reach convergence, even
after longer iterations. I tried much smaller values of
mixing beta which improves the final value of the error, but
I still cannot reach convergence on 100 iterations. As shown
in the mixbeta2_zoom.png, the error reduces to smaller
values around ~1e-5~1e-6, but it keeps stalling after a
while. I do not observe a well-converging behaviour for any
value.</p>
<p><br>
</p>
<p>I attached the "default version" of my script on which the
various modifications described above have been
independently performed. I obtained the geometry from a CIF
file in literature and checked it with visualization
software; it seems perfectly ok as far as I can tell.<br>
</p>
<p><br>
</p>
<p>Any insight on what I did wrong would be really helpful. I
suspect a shameful beginner mistake, but can not find it
out.<br>
</p>
<p><br>
</p>
<p>Thanks in advance,</p>
<p>Julien barbaud</p>
<p><br>
</p>
<p>P.S: this is my first time posting on this user list.
Please let me know if my question is not suitable for it, or
can be improved either in its content or presentation. I
will gladly take any recommandation into account in order
not to negatively impact the quality of this user list !<br>
</p>
</div>
</div>
<br>
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<br>
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