<div dir="ltr">Dear Guido and Giuseppe,<div><br></div><div>Thank you both for your replies. </div><div><br></div><div>The structure should be ok, it represents an organic molecule between 2 gold electrodes. You should get something like the image I attach (do you?). It is a rather standard scheme, as you may also see in: </div><div><br></div><div><a href="http://pubs.acs.org/doi/abs/10.1021/ja2090096">http://pubs.acs.org/doi/abs/10.1021/ja2090096</a></div><div><br></div><div>although my structure is simplified for testing.</div><div><br></div><div>I don't know whether ibrav=0 is strictly necessary but, anyway, it should not affect the outcome of the calculation, right? </div><div><br></div><div>I have tested other k-point meshes without improvement. Anyway, I'll try denser meshes together with Giuseppe's suggestions and let you know the outcome.</div><div><br></div><div>Cheers,</div><div>Sergi</div></div><div class="gmail_extra"><br><div class="gmail_quote">2015-02-03 13:56 GMT+01:00 Giuseppe Mattioli <span dir="ltr"><<a href="mailto:giuseppe.mattioli@ism.cnr.it" target="_blank">giuseppe.mattioli@ism.cnr.it</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><br>
Dear Sergi<br>
It seems that you bounce between more than one electronic configuration at every scf step. This is far from uncommon in the case of molecular open<br>
shell systems. :-(<br>
I can add one or two things to Guido's good advice.<br>
<span class=""><br>
> I've tried several tricks to try to improve electronic structure's<br>
> convergence. Changing the 'mixing_beta', the 'type of mixing', removing the<br>
> smearing,<br>
<br>
</span>Use always the more robust gaussian smearing (at least 0.01 Ry, but also more if you struggle for convergence) for geometry optimizations. If it does<br>
not converge, then m-p and m-v will also fail 99.9% . You can use other schemes after you tamed the system. Reduce also the mixing_beta down to 0.05<br>
or 0.02 (with davidson).<br>
<br>
Maybe your starting configuration is horribly unlucky. Try (carefully) to use something like<br>
<br>
conv_thr=1.0d-5~1.0d-6<br>
electron_maxstep=50~100<br>
scf_must_converge=.false.<br>
<br>
and see if your convergence problem improves after few bfgs steps without showing unphysical behavior.<br>
<br>
If your SOMO is higher than the Ag Fermi energy, then there is probably no way to have an integer value for the magnetization of the system because of<br>
the molecule-to-surface charge transfer. You may try not to bias the tot_magnetization variable.<br>
<br>
Finally, ecutwfc=25.0 seems a bit too low. It could be a source of instability. I would use something around 35/280 Ry for ecutwfc and ecutrho.<br>
<br>
HTH<br>
Giuseppe<br>
<div><div class="h5"><br>
<br>
On Tuesday, February 03, 2015 10:57:23 AM Sergi Vela wrote:<br>
> Hi all,<br>
><br>
> I'm having a lot of troubles in modeling the adsorption of molecules on<br>
> surfaces. I've quite a lot of experience with QE when working with crystals<br>
> made of open-shell molecules but I'm not familiar with the description of<br>
> metal surfaces.<br>
><br>
> First of all, I'm using Qespresso v.5.1.1<br>
><br>
> I succeed in simulating 4 layers of a 111 Gold surface with Quantum<br>
> Espresso (QE). However, using the same surface and unit cell, when I<br>
> include a magnetic (open-shell) molecule on top of that surface, even if<br>
> its far away from it, I cannot reach convergence. I'm 99% sure that the<br>
> input is fine in terms of the unit cell definition (see input file<br>
> attached) and the problem is just the convergence of the electronic<br>
> structure.<br>
><br>
> I believe the problem is the fact that the system is highly inhomogeneous<br>
> as it has a metal surface and an open-shell molecule. I take as an example<br>
> the smearing, since, although it is mandatory when modeling the metal<br>
> alone, it seems to hinder the description of an open-shell molecule.<br>
> Originally, I used methfessel-paxton smearing with a 'degauss' of 0.2 eV.<br>
> The convergence seems to be even worse as the value is increased, and<br>
> changing the type of smearing doesn't help neither.<br>
><br>
> I've tried several tricks to try to improve electronic structure's<br>
> convergence. Changing the 'mixing_beta', the 'type of mixing', removing the<br>
> smearing, switching to 'cg' algorith, increasing number K points ... all of<br>
> them with identical output (take Summary.out as an example of the typical<br>
> evolution of the SCF energy, you'll see that is awful).<br>
><br>
> Anyone has experience on modeling such king of systems?<br>
><br>
> Any help is appreciated, thanks in advance<br>
><br>
> Dr. Sergi Vela,<br>
> University of Strasbourg, France.<br>
<br>
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