<div dir="ltr">Strictly speaking, you should get convergence of the clean slab first, concerning both the slab thickness and the vacuum. Consider that thin slabs might suffer from "quantum confinement" effects, so it is important to look at the changes of the electronic properties if you are interested in accurately reproducing them, especialy as far as 'bulk' states are concerned.<div><br></div><div>Once you place a molecule on the slab, you should take care of the fact that the molecule "thickness" in the direction perpendicular to the slab actually corresponds to decreasing the vacuum width. As such, you should add to the vacuum this thickness, even approximately, to avoid what you mention.</div><div><br></div><div>Also consider that, if you want to get rid of effects of the slab asymmetry once the molecule has been placed on the slab, you should include dipole corrections. The alternative is to build a symmetric slab+molecule system, where the molecule is on both sides of the slab, which however is much more computationally expensive, because it requires a large unit cell size in the direction perpendicular to the slab.</div><div><br></div><div>Giovanni<br><div><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><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></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Il giorno lun 19 dic 2022 alle ore 10:32 Léon Luntadila Lufungula <<a href="mailto:Luntadilatiti@hotmail.com">Luntadilatiti@hotmail.com</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"><div class="msg3693839841955617207">
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<p class="MsoNormal"><span lang="EN-US">Dear QE users,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">I’m creating a slab for studying adsorption of small molecules (around 6-8 atoms in length) and want to converge both the slab thickness and vacuum width. However, I don’t fully understand how to do this properly… For
the convergence of the slab thickness, I was thinking about taking slabs of different thickness and calculating the surface energy and look at when the difference between two consecutive surface energies is smaller than 1 kcal/mol (i.e. chemical accuracy),
but I’ve also heard that you can look at the difference in energy when adding a layer and converging this energy difference to chemical accuracy. Any suggestions on which is the better option? For the vacuum width, I’m confused if you should converge this
value on a clean slab or on a slab with a model compound adsorbed onto it. I’ve been told you should do this on a clean slab, but I would expect that once an adsorbate is bonded onto the surface, the end of the adsorbate might be close enough to the next layer
to interact with it, which would make the convergence test obsolete…<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">I would be most thankful if someone could tell me the correct procedure in this situation!<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">Thanks in advance and kind regards,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">Léon Luntadila Lufungula<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">Structural Chemistry group<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">University of Antwerp<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
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