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<div class="">Sorry for my ignorance, but I still don’t see the point.</div>
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<div class="">Maybe a reference to some literature might help.</div>
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Met vriendelijke groeten,</div>
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Mit freundlichen Grüßen,</div>
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With kind regards,</div>
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Willem Offermans</div>
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Researcher Electrocatalysis SCT</div>
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VITO NV | Boeretang 200 | 2400 Mol</div>
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<div class="">On 11 Jan 2019, at 09:58, Malte Sachs <<a href="mailto:malte.sachs@chemie.uni-marburg.de" class="">malte.sachs@chemie.uni-marburg.de</a>> wrote:</div>
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<div class="moz-cite-prefix">Dear Willem,</div>
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<div class="moz-cite-prefix">in case of a screw axis or a glide plane you couple a rotation or a mirrow with a fractional translation (e.g. 1/2 or 1/3 of a lattice vector).</div>
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<div class="moz-cite-prefix">Best,<br class="">
Malte<br class="">
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<div class="moz-cite-prefix">Am 11.01.2019 um 09:03 schrieb Offermans Willem:<br class="">
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<blockquote type="cite" cite="mid:8A106270-707F-44F2-B63E-D6FEB49B4946@Vito.be" class="">
<div class="">Dear Paolo and Quantum Espresso friends,</div>
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<div class="">I’m sorry, but your explanation did not enlighten me. </div>
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<div class="">Your response: "it means that the symmetry operation consists in a rotation (or a rotation + spatial inversion) plus a translation (not a lattice one)” don’t ring a bell. </div>
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<div class="">What kind of translational symmetry are you talking about, if not the lattice one?</div>
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<div class="">My system has S2-Symmetry. This means a rotation about 180<span style="caret-color: rgb(34, 34, 34); color:
rgb(34, 34, 34); font-family: sans-serif; font-size: 14px;
background-color: rgb(255, 255, 255);" class="">°</span>, <span class="">followed
by reflection in a plane perpendicular to the rotation axis. It can be shortened to an inversion centre. Combined with the identity operation, this leads to 2 </span>Sym.Ops, which have been detected by the program. This is consistent with the message in the
output. Since I’m dealing with a slab, the system also has translational symmetry. I don’t see why the inversion centre should be incommensurate with this translational symmetry.</div>
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<div class="">What is the connection to the FFT grid?</div>
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<div class="">Met vriendelijke groeten,<br class="">
Mit freundlichen Grüßen,<br class="">
With kind regards,<br class="">
<br class="">
<br class="">
Willem Offermans<br class="">
Researcher Electrocatalysis SCT<br class="">
VITO NV | Boeretang 200 | 2400 Mol<br class="">
Phone:+32(0)14335263 Mobile:+32(0)492182073 <br class="">
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<div class="">On 10 Jan 2019, at 22:00, Paolo Giannozzi <<a href="mailto:p.giannozzi@gmail.com" class="" moz-do-not-send="true">p.giannozzi@gmail.com</a>> wrote:</div>
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<div dir="ltr" class="">On Thu, Jan 10, 2019 at 4:30 PM Offermans Willem <<a href="mailto:willem.offermans@vito.be" class="" moz-do-not-send="true">willem.offermans@vito.be</a>> wrote:</div>
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<div class=""> 2 Sym. Ops., with inversion, found ( 1 have fractional translation) </div>
[...] What does it mean?</div>
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<div class="">it means that the symmetry operation consists in a rotation (or a rotation + spatial inversion) plus a translation (not a lattice one)<br class="">
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<div class="">At some point in the sequence of calculations, the output contained the following message about symmetry:</div>
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<div class=""> No symmetry found</div>
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<div class="">I was surprised about the lost of symmetry. Is it related to the fractional translation?</div>
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<div class="">no, unless this happens in the last scf step, in which the FFT grid may change, in which case this is what may happen:</div>
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<div style="overflow-wrap: break-word;" class=""> (note: 1 additional sym.ops. were found but ignored
<div class=""> their fractional translations are incommensurate with FFT grid)</div>
<div class="">Paolo<br class="" clear="all">
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-- <br class="">
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<div class="">Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,<br class="">
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy<br class="">
Phone +39-0432-558216, fax +39-0432-558222<br class="">
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