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<div class="moz-cite-prefix">Dear Willem,</div>
<div class="moz-cite-prefix"><br>
</div>
<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>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Best,<br>
Malte<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix"><br>
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<div class="moz-cite-prefix">Am 11.01.2019 um 09:03 schrieb
Offermans Willem:<br>
</div>
<blockquote type="cite"
cite="mid:8A106270-707F-44F2-B63E-D6FEB49B4946@Vito.be">
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<div class="">Dear Paolo and Quantum Espresso friends,</div>
<div class=""><br class="">
</div>
<div class="">I’m sorry, but your explanation did not enlighten
me. </div>
<div class=""><br class="">
</div>
<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>
<div class=""><br class="">
</div>
<div class="">What kind of translational symmetry are you talking
about, if not the lattice one?</div>
<div class=""><br class="">
</div>
<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>
<div class=""><br class="">
</div>
<div class="">What is the connection to the FFT grid?</div>
<div class=""><br class="">
</div>
<div class=""><br class="">
</div>
<div class=""><br class="">
</div>
<div class=""> </div>
<span class=""><br class="">
</span><span class="">
<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="">
<br class="">
<a href="mailto:Willem.Offermans@Vito.be" class=""
moz-do-not-send="true">Willem.Offermans@Vito.be</a><br
class="">
<span style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0);
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src="cid:part2.9861BE7F.B9B43AFE@chemie.uni-marburg.de"
class=""></span>
</span></span><br class="">
</div>
</span>
<div><br class="">
<blockquote type="cite" class="">
<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>
<br class="Apple-interchange-newline">
<div class="">
<div dir="ltr" class="">
<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>
<div dir="ltr" class=""><br class="">
</div>
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0px 0px
0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div style="overflow-wrap: break-word;" class="">
<div class="">
<div class=""> 2 Sym. Ops., with inversion,
found ( 1 have fractional translation) </div>
[...] What does it mean?</div>
</div>
</blockquote>
<div class=""><br class="">
</div>
<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="">
</div>
<div class=""><br class="">
</div>
<blockquote class="gmail_quote" style="margin:0px 0px
0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div style="overflow-wrap: break-word;" class="">
<div class="">
<div class="">At some point in the sequence of
calculations, the output contained the following
message about symmetry:</div>
<div class=""><br class="">
</div>
<div class=""> No symmetry found</div>
<div class=""><br class="">
</div>
<div class="">I was surprised about the lost of
symmetry. Is it related to the fractional
translation?</div>
</div>
</div>
</blockquote>
<div class=""><br class="">
</div>
<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>
<div class=""><br class="">
</div>
<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">
</div>
</div>
</div>
-- <br class="">
<div dir="ltr" class="gmail_signature">
<div dir="ltr" class="">
<div class="">
<div dir="ltr" class="">
<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="">
<br class="">
</div>
</div>
</div>
</div>
</div>
</div>
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