<div dir="ltr"><div dir="ltr"><div><div dir="auto"><div><div><div><div dir="auto"><div><div><p>Dear Prof. Giovanni,</p><p>Thank you for your detailed response; I truly appreciate the time you took to explain everything thoroughly.</p><p>I used vc-relaxed cell parameters with a slight modification in a2 (a(2)_x = -1/2, a(2)_y = sqrt(3a/2), while the atomic_positions were taken from VS₂. Then, I performed vc-relax again. Now, the structure is preserving symmetry.</p></div></div></div></div></div></div></div></div><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Mar 4, 2025 at 3:15 PM Giovanni Cantele <<a href="mailto:giovanni.cantele@spin.cnr.it" target="_blank">giovanni.cantele@spin.cnr.it</a>> wrote:<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 dir="ltr"><div>The number of k-points is reduced or not reduced according to symmetries. So, if for two systems that should be exactly equivalent,</div><div>symmetries are different, that means that either atomic positions are different, or lattices are different or both.</div><div>Consider that symmetries are checked according to a threshold. I'm not very aware of that, but for sure what the code does is to</div><div>apply symmetry matrices to atomic positions and then compare the obtained positions with the initial ones (that should differ by at most lattice translations).</div><div>When a comparison is carried out, a threshold is setup, in that quantities (in our case atomic positions) are considered numerically the same if they differ</div><div>by less than the threshold.</div><div><br></div><div>Now, in your case, the first think that comes to the eye is :</div><div>vs2_nscf.out: 12 Sym. Ops. (no inversion) found<br>vse2_nscf.out: 2 Sym. Ops. (no inversion) found</div><div><br></div><div>So, the two systems definitely have different symmetries, so they are different! </div><div>After a closer inspection in the output files (similar conclusion could be drawn</div><div>from input files) we see that:</div><div>vs2_nscf.out:</div><div> crystal axes: (cart. coord. in units of alat)<br> a(1) = ( 1.000000 0.000000 0.000000 )<br> a(2) = ( -0.500000 0.866025 0.000000 )</div><div><br></div><div>vse2_nscf.out:</div><div> crystal axes: (cart. coord. in units of alat)<br> a(1) = ( 1.000000 0.000000 0.000000 )<br> a(2) = ( -0.500097 0.866068 0.000000 )</div><div><br></div><div>As you might see, while in the first case a(2)_x = -1/2, a(2)_y = sqrt(3)/2, in the second case there are little deviations</div><div>in the last digits that should be enough to prevent pw.x from finding symmetries in the second case.</div><div><br></div><div>As a general rule, if I know that a systems is hexagonal, I wouldn't use ibrav = 0 if there is a setting (ibrav = 4) that does the job for you!</div><div><br></div><div>As you said that you tried ibrav = 4, in that case what could be happened is that you forgot to change the atomic positions as well. Indeed,</div><div>those positions are in crystal units, so they were referred to axes that were very close to but not exactly (within the threshold) hexagonal ones. So, </div><div>he symmetry check, that in the first case was failing because of the crystal axes, in the second one is likely to fail because of the atomic positions.</div><div><br></div><div>Use in the second case ibrav = 4 and exactly the same (in-plane) atomic positions as in the first case, and for sure you'll get the same symmetries.</div><div><br></div><div>Giovanni</div><div><div dir="ltr" class="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><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Il giorno lun 3 mar 2025 alle ore 17:19 Zimmi Singh <<a href="mailto:singh.60@kgpian.iitkgp.ac.in" target="_blank">singh.60@kgpian.iitkgp.ac.in</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 dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div><span dir="ltr" style="min-height:0px"><span>Dear QE Community, <br></span></span></div><div><span dir="ltr" style="min-height:0px"><br></span></div><div>I am facing an unexpected discrepancy in k-point sampling during calculations for VS₂ and VSe₂, both of which have hexagonal symmetry. I
used the same Monkhorst-Pack k-point grid (<code>K_POINTS automatic 18x18x1</code>) for both, yet the number of k-points in the irreducible Brillouin zone (IBZ) differs significantly:</div><div><span dir="ltr" style="min-height:0px"><span><ul dir="ltr"><li dir="auto"><span>VS₂: 37 k-points</span></li><li dir="auto"><span>VSe₂: 164 k-points</span></li></ul></span><span>
</span><span></span></span></div><div>To investigate, I also defined the lattice structure of VSe₂ using <code>ibrav=4</code>, but the IBZ k-point count remains 164. I have attached the nscf input and output files for both systems for reference.</div>I would appreciate any insights on this matter, particularly on how to
reduce the IBZ k-points for VSe₂, as it is critical for GW calculations.
I also appreciate your time and suggestions.</div><div dir="ltr"><span class="gmail_signature_prefix"><br></span></div><div dir="ltr"><span class="gmail_signature_prefix">-- </span><br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><b><font><font>Best Regards</font></font></b></div><div><span style="color:rgb(68,68,68)"><span style="background-color:rgb(255,255,255)"><font><font>Zimmi Singh</font></font></span></span></div><div><span style="color:rgb(68,68,68)"><span style="background-color:rgb(255,255,255)"><i><font><font>Research_Scholar <br></font></font></i></span></span></div><div><span style="color:rgb(68,68,68)"><i>Department of Metallurgical and Materials Engineering<br>
Indian Institute of Technology, Kharagpur<br>
Kharagpur, India</i></span></div><div><font><font><br></font></font></div></div></div></div></div></div></div>
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The Quantum ESPRESSO Foundation stands in solidarity with all civilians worldwide who are victims of terrorism, military aggression, and indiscriminate warfare.<br>
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Quantum ESPRESSO is supported by MaX (<a href="http://www.max-centre.eu" rel="noreferrer" target="_blank">www.max-centre.eu</a>)<br>
users mailing list <a href="mailto:users@lists.quantum-espresso.org" target="_blank">users@lists.quantum-espresso.org</a><br>
<a href="https://lists.quantum-espresso.org/mailman/listinfo/users" rel="noreferrer" target="_blank">https://lists.quantum-espresso.org/mailman/listinfo/users</a></blockquote></div><div><br clear="all"></div><br><span class="gmail_signature_prefix">-- </span><br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><b><font><font>Best Regards</font></font></b></div><div><span style="color:rgb(68,68,68)"><span style="background-color:rgb(255,255,255)"><font><font>Zimmi Singh</font></font></span></span></div><div><span style="color:rgb(68,68,68)"><span style="background-color:rgb(255,255,255)"><i><font><font>Research_Scholar <br></font></font></i></span></span></div><div><span style="color:rgb(68,68,68)"><i>Department of Metallurgical and Materials Engineering<br>
Indian Institute of Technology, Kharagpur<br>
Kharagpur, India</i></span></div><div><font><font><br></font></font></div></div></div>
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