<div dir="ltr">Let us suppose that we have a fcc crystal, with one atom per cell, at (0,0,0), for the sake of simplicity.<div><br></div><div>The unit cell sides are in the form (a/2,a/2,0) (a=side of the cubic cell), with unit cell volume a^3 / 4.</div><div><br></div><div>Now, let us move from fcc to sc unit cell. </div><div>Each of the 8 atoms at the corners is shared by 8 cubic cells, and thus we should consider only one of these atoms.</div><div>On the other hand, atoms at the center of the cube faces are shared by two unit cells, and count as 1/2. Since we have</div><div>6 faces, 3 out of these 6 atoms must be considered.</div><div>As a result, the sc unit cell will contain 4 atoms and a volume 4 times larger, a^3 as you would expect.</div><div><br></div><div>To go back from sc to fcc you should therefore keep 1/4 of your atoms, because those that are associated to the centers of three faces,</div><div>that should be explicitly considered in sc, now become equivalent (that is, connected by a lattice vector) to other atoms in fcc.</div><div><br></div><div>The code correctly finds overlapped atoms, e.g. in the example of one atom per unit cell, in sc you would have (0,0,0), (a/2,a/2,0), (a/2,0,a/2), (0,a/2,a/2)</div><div>and the last three in fcc are obtained from (0,0,0) after a lattice translation by (a/2,a/2,0), (a/2,0,a/2), (0,a/2,a/2), respectively.</div><div><br></div><div>Giovanni</div><div><br></div><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><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Il giorno mar 27 feb 2024 alle ore 11:14 Ms. Chandrika K. via users <<a href="mailto:users@lists.quantum-espresso.org">users@lists.quantum-espresso.org</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="msg6712331141618266395">
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<div><span style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">Need help in understanding </span></div>
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<span style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">I am currently working on Co3O4 structure,from literature it is very evident that it belongs to space group Fd3m(cubic
fcc).</span></li><li style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
<div style="margin:0px"><span style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">I have referred to Co3O4 Fd3m cubic structure from materials project
it is represented as simple cubic structure but Fd3m space group refers to cubic fcc.</span></div>
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<div style="margin:0px"><span style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">As it is simple cubic ibrav =1,when i change ibrav =2(cubic fcc)
i am getting warning message </span></div>
<div style="margin:0px"><span style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">"WARNING: Atom 381 and atom 444 are very close !!! Atom 444 deleted
!!!"</span></div>
<div style="margin:0px"><span style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">ATOMIC_POSITIONS (angstrom)</span></div>
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I would like to know how to change the structure from simple cubic to fcc cubic</div>
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chandrika yadav k </div>
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