<div dir="ltr"><div dir="ltr">Quick google search: <a href="http://quantum.phys.cmu.edu/groupth/gt21.pdf">http://quantum.phys.cmu.edu/groupth/gt21.pdf</a><br></div></div><br><div class="gmail_quote"><div dir="ltr">On Fri, Jan 11, 2019 at 10:23 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>Sorry for my ignorance, but I still don’t see the point.</div>
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<div>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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<div>On 11 Jan 2019, at 09:58, Malte Sachs <<a href="mailto:malte.sachs@chemie.uni-marburg.de" target="_blank">malte.sachs@chemie.uni-marburg.de</a>> wrote:</div>
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<div class="gmail-m_6435918764872608877moz-cite-prefix">Dear Willem,</div>
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<div class="gmail-m_6435918764872608877moz-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="gmail-m_6435918764872608877moz-cite-prefix">Best,<br>
Malte<br>
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<div class="gmail-m_6435918764872608877moz-cite-prefix">Am 11.01.2019 um 09:03 schrieb Offermans Willem:<br>
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<div>Dear Paolo and Quantum Espresso friends,</div>
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<div>I’m sorry, but your explanation did not enlighten me. </div>
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<div>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>What kind of translational symmetry are you talking about, if not the lattice one?</div>
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<div>My system has S2-Symmetry. This means a rotation about 180<span style="color:rgb(34,34,34);font-family:sans-serif;font-size:14px;background-color:rgb(255,255,255)">°</span>, <span>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>What is the connection to the FFT grid?</div>
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<div>Met vriendelijke groeten,<br>
Mit freundlichen Grüßen,<br>
With kind regards,<br>
<br>
<br>
Willem Offermans<br>
Researcher Electrocatalysis SCT<br>
VITO NV | Boeretang 200 | 2400 Mol<br>
Phone:+32(0)14335263 Mobile:+32(0)492182073 <br>
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<a href="mailto:Willem.Offermans@Vito.be" target="_blank">Willem.Offermans@Vito.be</a><br>
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<div>On 10 Jan 2019, at 22:00, Paolo Giannozzi <<a href="mailto:p.giannozzi@gmail.com" target="_blank">p.giannozzi@gmail.com</a>> wrote:</div>
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<div dir="ltr">On Thu, Jan 10, 2019 at 4:30 PM Offermans Willem <<a href="mailto:willem.offermans@vito.be" target="_blank">willem.offermans@vito.be</a>> wrote:</div>
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<div>     2 Sym. Ops., with inversion, found ( 1 have fractional translation) </div>
[...] What does it mean?</div>
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<div>it means that the symmetry operation consists in a rotation (or a rotation + spatial inversion) plus a translation (not a lattice one)<br>
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<div>At some point in the sequence of calculations, the output contained the following message about symmetry:</div>
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<div>    No symmetry found</div>
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<div>I was surprised about the lost of symmetry. Is it related to the fractional translation?</div>
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<div>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>          (note:  1 additional sym.ops. were found but ignored
<div>           their fractional translations are incommensurate with FFT grid)</div>
<div>Paolo<br clear="all">
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<div>Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,<br>
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy<br>
Phone +39-0432-558216, fax +39-0432-558222<br>
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