<div dir="ltr"><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><span style="color:rgb(0,0,0)">Hi, I do not have a precise explanation of that, but I can say that I found such a behavior several times, in the years,</span></div><div><span style="color:rgb(0,0,0)">for completely different systems. </span></div><div><span style="color:rgb(0,0,0)">And this concerns not only the convergence of the scf step, but also the relaxation</span></div><div><span style="color:rgb(0,0,0)">of the atomic positions. </span></div><div><span style="color:rgb(0,0,0)">At some iteration it seems that the algorithm falls in some "potential well" and cannot exit it at all.</span></div><div><span style="color:rgb(0,0,0)"><br></span></div><div><span style="color:rgb(0,0,0)">In this respect, it helps often just to restart the calculation from scratch using one of the last coordinate sets found by</span></div><div><span style="color:rgb(0,0,0)">the pw.x, or in some cases restart the code introducing in the coordinates even very small perturbations (e.g. delete the</span></div><div><font color="#000000">digits from the fourth to the last). In other cases, you might try to increase the smearing, even just for a few steps, mostly if</font></div><div><font color="#000000">the problem is the convergence of the scf cycle.</font></div><div><font color="#000000">This is just empirical, but it is the signature for tricky calculations (where there is no parameter</font></div><div><font color="#000000">to identify when a calculation is going to become "tricky"!), where the presence of local minima or other numerically hard problems, </font></div><div><font color="#000000">either with respect to the charge density or with respect to the atomic positions, can make the convergence non as easy as expected.</font></div><div><font color="#000000"><br></font></div><div><font color="#000000">Maybe, someone more expert might add some more specific hints.</font></div><div><font color="#000000"><br></font></div><div><font color="#000000">Giovanni</font></div><div dir="ltr"><span style="color:rgb(0,0,0)"><br></span></div><div dir="ltr"><span style="color:rgb(0,0,0)">-- <br><br>Giovanni Cantele, PhD<br>CNR-SPIN<br>c/o Dipartimento di Fisica<br>Universita' di Napoli "Federico II"<br>Complesso Universitario M. S. Angelo - Ed. 6<br>Via Cintia, I-80126, Napoli, Italy<br><a href="mailto:giovanni.cantele@spin.cnr.it" style="color:rgb(17,85,204)" target="_blank">e-mail: giovanni.cantele@spin.cnr.it</a><br>Phone: +39 081 676910<br>Skype contact: giocan74<br><br>ResearcherID: <a href="http://www.researcherid.com/rid/A-1951-2009" style="color:rgb(17,85,204)" target="_blank">http://www.researcherid.com/rid/A-1951-2009</a><br>Web page: </span><a href="https://sites.google.com/view/giovanni-cantele/home" style="color:rgb(17,85,204)" target="_blank">https://sites.google.com/view/giovanni-cantele/home</a><br></div></div></div><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Il giorno mar 19 dic 2023 alle ore 08:49 Laurent Pizzagalli <<a href="mailto:laurent.pizzagalli@univ-poitiers.fr">laurent.pizzagalli@univ-poitiers.fr</a>> ha scritto:<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 all,<br>
<br>
I came across an issue I never encountered before. I performed a simple <br>
ionic relaxation of a W cluster. The initial scf convergence is <br>
achieved, the ionic forces are calculated (and are reasonable for a <br>
first ionic relaxation step) and the new atomic positions are obtained. <br>
The issue arises during the next scf calculation, which diverges in a <br>
few steps. However, if I start a new calculation with the updated ionic <br>
positions as input structure, the scf calculation runs smoothly and <br>
converges (but the issue occurred again for the next ionic relaxation <br>
steps).<br>
I obtained the same behavior with two different pw.x versions (6.7 and <br>
7.1). I also tried to set 'pot_extrapolation = none', but with no <br>
difference...<br>
<br>
Do any of you have an idea about the origin (and solution) of this issue ?<br>
<br>
Thanks<br>
<br>
Laurent<br>
<br>
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