<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">You should figure out how the two materials match at the interface. This can be straightforward or quite hard, depending on the system.<div class="">If the metallic substrate surface is described by the same Bravais lattice as the semiconductor (e.g. you are interfacing two cubic or two</div><div class="">hexagonal materials), you easily choose the surface unit cell and must take care only of the lattice parameter. One choice is based on the fact that,</div><div class="">if one of the two materials plays the role of the substrate and a thin layer of the other material is deposited on top, you expect that the thin layer</div><div class="">will not significantly modify the thick substrate lattice parameter, and you use the substrate lattice parameters. If this is not the case, the lattice parameters</div><div class="">choice will depend on the specific system, and you could eventually choose to optimise them to get the lowest energy interface.</div><div class=""><br class=""></div><div class="">There are other interfaces where also the choice of the surface Bravais lattice is not straightforward because it requires to appropriately identify</div><div class="">surface supercells of both materials, in some cases after a rotation of one of the two.</div><div class=""><br class=""></div><div class="">You might find lot of examples in the literature, just to mention one I studied some year ago [J. Phys.: Condens. Matter 27 (2015) 015006], if you</div><div class="">interface the ZnO (0001) surface with the (111) surface of metals like Ag, Al, Pd, Pt, both have an hexagonal unit cell, so you can easily build for </div><div class="">both the 1x1 surface hexagonal unit cell. However, it turns out that the two lattice parameters are quite different, thus resulting in a significant</div><div class="">mismatch at the interface, inducing strain that can modify the interface properties. A much lower interface mismatch is obtained by matching</div><div class="">the sqrt(3) x sqrt(3) R30 ZnO(0001) surface, with the 2x2 metal (111) surface. The former is obtained after a suitable rotation of the ZnO (see Fig. 2</div><div class="">of the mentioned paper).</div><div class="">This has nothing to do with what you want to study, but is to mention an example of what one should have in mind when setting up the surface</div><div class="">unit cell of an interface.</div><div class=""><br class=""></div><div class="">One you identify the geometry of your interface, than it is easy to set up the QE calculation, you choose the ibrav value that fits your needs (in the mentioned</div><div class="">example hexagonal lattice), with special care on the lattice parameter in the direction perpendicular to the surface, because a sufficiently large</div><div class="">vacuum space must separate two periodic replicas of the slab to avoid spurious interactions. If in the place of specifying the lattice using ibrav>0 and celldm(*)</div><div class="">you choose to use the CELL_PARAMETERS card, then you must just identify the three lattice vectors that describe the slab supercell, both in the directions</div><div class="">parallel and perpendicular to the surface (so they are still three three-dimensional vectors).</div><div class=""><br class=""></div><div class="">Concerning degauss, it is quite likely that if you start from a metal and a semiconductor, the metal will remain a metal after the interface is formed, so you</div><div class="">use degauss just in the same way as you do for calculation of the bulk metal.</div><div class=""><br class=""></div><div class="">More help could be provided if you give more details about the system you want to investigate.</div><div class=""><br class=""></div><div class="">Giovanni</div><div class=""><div class=""><br class=""></div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On 21 Sep 2016, at 18:52, Lorenzo Pedrazzetti <<a href="mailto:lorenzo.pedrazzetti@polimi.it" class="">lorenzo.pedrazzetti@polimi.it</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Arial; font-size: 12pt;" class="">Thanks everyone for the advices.<br class="">But I think I am facing a bigger problem. I would like to analyse the interface between a metal and a semiconductor, but many issues come to my mind:<br class="">1. how should I define the system? I will have a system requiring smearing while the other won't;<br class="">2.how to relate celldm() to the correct system?<br class="">3.still the building of "CELL_PARAMETERS" card is obsure to me for this kind of mixed system.<br class="">Thank anyone who wants to help.<br class="">Lorenzo.<br class=""><br class="">Sent from my ASUS</span><span style="font-family: Arial;" class=""><br class=""><br class="">-------- Messaggio originale --------<br class="">Da:Giuseppe Mattioli<span class="Apple-converted-space"> </span><br class="">Inviato:Wed, 21 Sep 2016 15:39:03 +0200<br class="">A:<a href="mailto:pw_forum@pwscf.org" class="">pw_forum@pwscf.org</a><br class="">Oggetto:Re: [Pw_forum] mixed supercells<br class=""><br class=""></span></div><font size="2" style="font-family: Helvetica; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-size: 10pt;" class=""><div class="PlainText"><br class="">And if you have no experimental hint of the behavior of cell parameters at the interface you can start by averaging the parameters, with a (hopefully<span class="Apple-converted-space"> </span><br class="">little) strain of both materials.<br class=""><br class="">HTH<br class=""><br class="">Giuseppe<span class="Apple-converted-space"> </span><br class=""><br class="">On Wednesday, September 21, 2016 03:09:49 PM Jess Wellendorff wrote:<br class="">> The VNL "Interface Builder" would make it very easy for you to build a<br class="">> minimum-strain interface:<br class="">><span class="Apple-converted-space"> </span><br class="">><span class="Apple-converted-space"> </span><a href="http://docs.quantumwise.com/tutorials/ag_au_interface/ag_au_interface.html" class="">http://docs.quantumwise.com/tutorials/ag_au_interface/ag_au_interface.html</a><br class="">><span class="Apple-converted-space"> </span><br class="">> On 09/21/2016 03:04 PM, Lorenzo Paulatto wrote:<br class="">> > Dear Lorenzo,<br class="">> > you cannot specify different periodicity, you have to build a<br class="">> > super-cell, as big as the 3x3 cell of the first material, or the 2x2<br class="">> > cell of the second, then you fill it with 9 units of the first<br class="">> > material and 4 of the other. This can be done by hand (the first time<br class="">> > it'll take you an hour or two), or there are some softwares that can<br class="">> > help you I have never used one, as hence I cannot recommend any.<br class="">> ><span class="Apple-converted-space"> </span><br class="">> ><span class="Apple-converted-space"> </span><br class="">> > On 21 September 2016 at 14:46, Lorenzo Pedrazzetti<br class="">> > <<a href="mailto:lorenzo.pedrazzetti@polimi.it" class="">lorenzo.pedrazzetti@polimi.it</a><span class="Apple-converted-space"> </span><<a href="mailto:lorenzo.pedrazzetti@polimi.it" class="">mailto:lorenzo.pedrazzetti@polimi.it</a>>><br class="">> ><span class="Apple-converted-space"> </span><br class="">> > wrote:<br class="">> > Good afternoon,<br class="">> > <span class="Apple-converted-space"> </span><br class="">> > I am trying to model the interface between two solid with<br class="">> > different cella parameter. By looking at their experimental cell<br class="">> > value I am supposed to stack a 3x3 slab onto a 2x2 slab made of<br class="">> > different material.<br class="">> > <span class="Apple-converted-space"> </span><br class="">> > My problemi s the “CELL_PARAMETERS†card; i found some<br class="">> > difficulties to understand how to specify the different<br class="">> > periodicity of the two materials.<br class="">> > <span class="Apple-converted-space"> </span><br class="">> > Thanks a lot,<br class="">> > <span class="Apple-converted-space"> </span><br class="">> > Lorenzo.<br class="">> > <span class="Apple-converted-space"> </span><br class="">> > <span class="Apple-converted-space"> </span><br class="">> > _______________________________________________<br class="">> > Pw_forum mailing list<br class="">> > <span class="Apple-converted-space"> </span><a href="mailto:Pw_forum@pwscf.org" class="">Pw_forum@pwscf.org</a><span class="Apple-converted-space"> </span><<a href="mailto:Pw_forum@pwscf.org" class="">mailto:Pw_forum@pwscf.org</a>><br class="">> > <span class="Apple-converted-space"> </span><a href="http://pwscf.org/mailman/listinfo/pw_forum" class="">http://pwscf.org/mailman/listinfo/pw_forum</a><br class="">> > <<a href="http://pwscf.org/mailman/listinfo/pw_forum" class="">http://pwscf.org/mailman/listinfo/pw_forum</a>><br class="">> ><span class="Apple-converted-space"> </span><br class="">> > _______________________________________________<br class="">> > Pw_forum mailing list<br class="">> ><span class="Apple-converted-space"> </span><a href="mailto:Pw_forum@pwscf.org" class="">Pw_forum@pwscf.org</a><br class="">> ><span class="Apple-converted-space"> </span><a href="http://pwscf.org/mailman/listinfo/pw_forum" class="">http://pwscf.org/mailman/listinfo/pw_forum</a><br class=""><br class="">********************************************************<br class="">- Article premier - Les hommes naissent et demeurent<br class="">libres et égaux en droits. Les distinctions sociales<br class="">ne peuvent être fondées que sur l'utilité commune<br class="">- Article 2 - Le but de toute association politique<br class="">est la conservation des droits naturels et<span class="Apple-converted-space"> </span><br class="">imprescriptibles de l'homme. Ces droits sont la liberté,<br class="">la propriété, la sûreté et la résistance à l'oppression.<br class="">********************************************************<br class=""><br class=""> Giuseppe Mattioli <span class="Apple-converted-space"> </span><br class=""> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA <span class="Apple-converted-space"> </span><br class=""> v. 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-- <br class=""><br class="">Giovanni Cantele, PhD<br class="">CNR-SPIN<br class="">c/o Dipartimento di Fisica<br class="">Universita' di Napoli "Federico II"<br class="">Complesso Universitario M. S. Angelo - Ed. 6<br class="">Via Cintia, I-80126, Napoli, Italy<br class="">e-mail: <a href="mailto:giovanni.cantele@spin.cnr.it" class="">giovanni.cantele@spin.cnr.it</a><br class="">Phone: +39 081 676910<br class="">Skype contact: giocan74<br class=""><br class="">ResearcherID: <a href="http://www.researcherid.com/rid/A-1951-2009" class="">http://www.researcherid.com/rid/A-1951-2009</a><br class="">Web page: <a href="http://people.na.infn.it/~cantele" class="">http://people.na.infn.it/~cantele</a><br class="">
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