<font face="Default Sans Serif,Verdana,Arial,Helvetica,sans-serif" size="2"> <span>hi mkondrin<br><br>the email below, from the author of cif2cell, explains the reasons for having<br>zero forces for all copper and chromium atoms on the basis of the CIF file site<br>symmetries; please find enclosed the cif file<br><br>regards<br><br>Manuel<br>PS the expected forces, qualitatively speaking are shown below (first 6 lines are oxygen, next three lines are Cr, last 3 lines are copper atoms), from a low cutoff, small number of k-points abinit calculation <br>(in the espresso calculation some copper and chromium atoms are fixed, other copper and chromium atoms move, which means some of the copper-copper, chromium-copper and chromium-chromium distances vary, and they</span><span> should all be fixed)<br> <br>cartesian forces (eV/Angstrom) at end:<br> 1 0.00000000000000 0.00000000000000 33.52744537217701<br> 2 0.00000000000000 0.00000000000000 33.52744537217701<br> 3 0.00000000000000 0.00000000000000 33.52744537217700<br> 4 0.00000000000000 0.00000000000000 -33.52744537217701<br> 5 0.00000000000000 0.00000000000000 -33.52744537217701<br> 6 0.00000000000000 0.00000000000000 -33.52744537217700<br> 7 0.00000000000000 0.00000000000000 0.00000000000000<br> 8 0.00000000000000 0.00000000000000 0.00000000000000<br> 9 0.00000000000000 0.00000000000000 0.00000000000000<br> 10 0.00000000000000 0.00000000000000 0.00000000000000<br> 11 0.00000000000000 0.00000000000000 0.00000000000000<br> 12 0.00000000000000 0.00000000000000 0.00000000000000<br><br>Dr Manuel Pérez Jigato, Chargé de Recherche<br>Luxembourg Institute of Science and Technology (LIST)<br>Materials Research and Technology (MRT)<br>41 rue du Brill<br>L-4422 BELVAUX<br>Grand-Duché de Luxembourg<br>Tel (+352) 47 02 61 - 584<br>Fax (+352) 47 02 64<br>e-mail manuel.perez@list.lu</span><br><br><font color="#990099">-----Forwarded by Manuel Pérez Jigato/LIST on 05/30/2015 06:35PM -----</font><div style="padding-left:5px;"><div style="padding-right:0px;padding-left:5px;border-left:solid black 2px;">To: Manuel Pérez Jigato <manuel.perez@list.lu><br>From: Björkman Torbjörn <torbjorn.bjorkman@aalto.fi><br>Date: 05/29/2015 02:04PM<br>Subject: SV: SV: SV: cif2cell enquiry<br><br>
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<div style="direction: ltr; font-family: Tahoma; font-size: 10pt;"><font color="#000000">Well, whether or not it is explicitly used for symmetrization, the symmetry is of course still there. So if by symmetry the forces should be zero, then they should be zero. In your
case I can see from the CIF that the forces should indeed be zero, since they are 3a and 3b Wyckoff positions, which have no free parameters. If they are not, then there is some form of numerical problem, how bad it is of course depends on how large the forces
are. The manual mentioned that the fourier mesh might not having the symmetry of the lattice in all cases, it may be that it is possible to get that in order by selecting them as multiples of 3 for a trigonal lattice. That's all I can say, I don't know anything
specific about QE.<br>
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Cheers,<br>
Torbjörn<br>
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Torbjörn Björkman, PhD<br>
COMP, Aalto University School of Science<br>
Espoo, Finland<br>
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<div style="direction: ltr;" id="divRpF789880"><font face="Tahoma" size="2" color="#000000"><b>Från:</b> Manuel Pérez Jigato [manuel.perez@list.lu]<br>
<b>Skickat:</b> den 29 maj 2015 14:42<br>
<b>Till:</b> Björkman Torbjörn<br>
<b>Ämne:</b> Re: SV: SV: cif2cell enquiry<br>
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<p><font face="sans-serif" size="2">thanks a lot Bjorkman, it is very kind of you</font><br>
<font face="sans-serif" size="2">my only worry would be the possible implications for the forces</font><br>
<font face="sans-serif" size="2">I will ask to the pwscf mailing list</font><br>
<font face="sans-serif" size="2">regards</font><br>
<font face="sans-serif" size="2">Manuel</font><br>
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<img src="cid:1__=4EBBF4C7DFD3A9AE8f9e8a93df938690@list.lu" alt="Inactive hide details for Björkman Torbjörn ---29/05/2015 12:08:34---Dear Manuel, I can find nothing that looks wrong in the ci" height="16" width="16" border="0"><font face="sans-serif" size="2" color="#424282">Björkman
Torbjörn ---29/05/2015 12:08:34---Dear Manuel, I can find nothing that looks wrong in the cif2cell output, but a quick look in the "Tr</font><br>
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<font face="sans-serif" size="1" color="#5F5F5F">From: </font><font face="sans-serif" size="1">Björkman Torbjörn <torbjorn.bjorkman@aalto.fi></font><br>
<font face="sans-serif" size="1" color="#5F5F5F">To: </font><font face="sans-serif" size="1">Manuel Pérez Jigato <manuel.perez@list.lu>,
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<font face="sans-serif" size="1" color="#5F5F5F">Date: </font><font face="sans-serif" size="1">29/05/2015 12:08</font><br>
<font face="sans-serif" size="1" color="#5F5F5F">Subject: </font><font face="sans-serif" size="1">SV: SV: cif2cell enquiry</font><br>
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<font face="Tahoma" size="2">Dear Manuel,<br>
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I can find nothing that looks wrong in the cif2cell output, but a quick look in the "Troubleshooting" section of the QE manual seems to provide the most likely answer:</font>
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<font face="serif" size="3">pw.x does not find all the symmetries you expected </font>
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<font face="Tahoma" size="2">...</font>
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<li><font face="serif" size="3">a fractional translation, without rotation, is a symmetry operation of the system. This means that the cell is actually a supercell. In this case, all symmetry operations containing fractional translations are disabled. The reason
is that in this rather exotic case there is no simple way to select those symmetry operations forming a true group, in the mathematical sense of the term.
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<font face="Tahoma" size="2">What they say is that QE in cases like these will just say "this is a supercell" and throw the fractional translations away, which gives you 12 symmetries instead of 36, just as it should. I have no idea if you can bypass this behaviour
in QE though, better ask on their mailing list.</font><br>
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Hope this helps,<br>
Torbjörn<br>
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<font face="Tahoma" size="1">---<br>
Torbjörn Björkman, PhD<br>
COMP, Aalto University School of Science<br>
Espoo, Finland<br>
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<font face="Tahoma" size="2"><b>Från:</b></font><font face="Tahoma" size="2"> Manuel Pérez Jigato [manuel.perez@list.lu]</font><font face="Tahoma" size="2"><b><br>
Skickat:</b></font><font face="Tahoma" size="2"> den 29 maj 2015 12:37</font><font face="Tahoma" size="2"><b><br>
Till:</b></font><font face="Tahoma" size="2"> Björkman Torbjörn</font><font face="Tahoma" size="2"><b><br>
Ämne:</b></font><font face="Tahoma" size="2"> Re: SV: cif2cell enquiry</font><font face="Roman" size="1"><br>
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<font face="sans-serif" size="2">Dear Bjorkman</font><font face="Roman" size="1"><br>
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thanks for your prompt reply<br>
please find enclosed the files</font><font face="Roman" size="1"><i>(See attached file: esta.cif)(See attached file: QE_NOREDUCE_esta.in)(See attached file: second.in)(See attached file: second.out)(See attached file: output_noreduce.txt)</i></font><font face="Roman" size="1"><br>
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Manuel<br>
PS the different between the two .in files is that one of them is the direct output from cif2cell, whilst the other is produced by<br>
adding a few options by hand, before running quantum-espresso (whose output you can see as well)</font><br>
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