<div dir="ltr">Willem,<div><br></div><div>Add the command</div><div><br></div>use_all_frac=.true.<div><br></div><div>to &system. IIRC, this adjusts the FFT grid to be commensurate.</div><div><br></div><div>Alternatively, you can set the values of the FFT grid (nr1, nr2, nr3) by hand. Depending on the fractional translation, making these integers multiples of 2, 3, 4, or 6 should solve your problem.</div><div><br></div><div>Note the warning in the PW documentation about when you shouldn't set use_all_frac</div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr">On Thu, Jan 10, 2019 at 10:30 AM Offermans Willem <<a href="mailto:willem.offermans@vito.be">willem.offermans@vito.be</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">
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<div>Dear Quantum Espresso friends,</div>
<div><br>
</div>
<div>All my systems of interest have S2-symmetry, i.e. there is an inversion centre present.</div>
<div>In one of my previous mails, I complained about loosing symmetry. I calculate my systems</div>
<div>sequently with increased accuracy. I clearly started with a system with an inversion centre.</div>
<div><br>
</div>
<div>There was a message in the output of the first calculation:</div>
<div><br>
</div>
<div> 2 Sym. Ops., with inversion, found ( 1 have fractional translation) </div>
<div><br>
</div>
<div>I realise now that I did not read this message carefully. I missed the last part about fractional translation.</div>
<div>What does it mean?</div>
<div><br>
</div>
<div>At some point in the sequence of calculations, the output contained the following message about symmetry:</div>
<div><br>
</div>
<div> No symmetry found</div>
<div><br>
</div>
<div>I was surprised about the lost of symmetry. Is it related to the fractional translation?</div>
<div><br>
</div>
<div><br>
</div>
<div>Today I put a lot of effort to impose the symmetry. I read one part of the system from output and generated</div>
<div>the other part by inversion.</div>
<div><br>
</div>
<div>Now the output contained the following message:</div>
<div><br>
</div>
<div> No symmetry found</div>
<div> (note: 1 additional sym.ops. were found but ignored</div>
<div> their fractional translations are incommensurate with FFT grid)</div>
</div>
<div><br>
</div>
<div>How can I bring the fractional translations of the sym.ops in commensurate mode with FFT grid?</div>
<div><br>
</div>
<br>
<div>
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Met vriendelijke groeten,</div>
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With kind regards,</div>
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