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<p><font size="2" face="sans-serif">Dear Nicola</font><br>
<br>
<font size="2" face="sans-serif">thanks a lot for your comments, your are right, your response was exactly the same than</font><br>
<font size="2" face="sans-serif">that by the author of cif2cell, ie ,the supercell extra symmetries are disregarded by pwscf</font><br>
<font size="2" face="sans-serif">and just the primitive cell symmetries are considered. Certainly, to compute point defects using </font><br>
<font size="2" face="sans-serif">supercells, you usually switch off all symmetries, so, it makes sense to use the converged conditions</font><br>
<font size="2" face="sans-serif">for the supercell and no symmetry at all. However, sometimes you need to spend some time</font><br>
<font size="2" face="sans-serif">doing convergence tests with intermediate size or smaller size supercells, and that means, usually </font><br>
<font size="2" face="sans-serif">working under low quality conditions</font><br>
<br>
<font size="2" face="sans-serif">From my point of view, as a newcomer to espresso, I am trying to see whether certain tests for</font><br>
<font size="2" face="sans-serif">convergence can be quickly carried out. Ideally, I would like to see all the symmetries present so</font><br>
<font size="2" face="sans-serif">that I can look at the forces even under low cutoff/small number of k-point conditions. The reason</font><br>
<font size="2" face="sans-serif">I asked this question to the forum is that in case the symmetry limitations for supercells could be</font><br>
<font size="2" face="sans-serif">overcome, this would be helpful for me. At the moment, it looks like the only way of having zero</font><br>
<font size="2" face="sans-serif">forces on certain atoms (in my case) is using converged parameters</font><br>
<br>
<font size="2" face="sans-serif">Regarding the 5x5x1 set of k-points, this is the smallest set I can think of, considering the (real space) lattice</font><br>
<font size="2" face="sans-serif">parameters I use keep more or less that ratio (inverted), and this set is certainly not converged...</font><br>
<br>
<font size="2" face="sans-serif">regards</font><br>
<br>
<font size="2" face="sans-serif">Manuel</font><br>
<br>
<font size="2" face="sans-serif">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<br>
</font><br>
<br>
<img width="16" height="16" src="cid:1__=4EBBF4C4DFA707418f9e8a93df938690@list.lu" border="0" alt="Inactive hide details for Nicola Marzari ---31/05/2015 11:51:53---Dear Manuel, Torbjörn is saying exactly the same thing I said"><font size="2" color="#424282" face="sans-serif">Nicola Marzari ---31/05/2015 11:51:53---Dear Manuel, Torbjörn is saying exactly the same thing I said, re fractional</font><br>
<br>
<font size="1" color="#5F5F5F" face="sans-serif">From: </font><font size="1" face="sans-serif">Nicola Marzari <nicola.marzari@epfl.ch></font><br>
<font size="1" color="#5F5F5F" face="sans-serif">To: </font><font size="1" face="sans-serif">PWSCF Forum <pw_forum@pwscf.org>, Manuel Pérez Jigato <perez@lippmann.lu>, </font><br>
<font size="1" color="#5F5F5F" face="sans-serif">Date: </font><font size="1" face="sans-serif">31/05/2015 11:51</font><br>
<font size="1" color="#5F5F5F" face="sans-serif">Subject: </font><font size="1" face="sans-serif">Re: [Pw_forum] Fw: SV: SV: SV: cif2cell enquiry TO MKONDRIN ( one file enclosed )</font><br>
<font size="1" color="#5F5F5F" face="sans-serif">Sent by: </font><font size="1" face="sans-serif">pw_forum-bounces@pwscf.org</font><br>
<hr width="100%" size="2" align="left" noshade style="color:#8091A5; "><br>
<br>
<br>
<tt><font size="2"><br>
<br>
<br>
Dear Manuel,<br>
<br>
<br>
Torbjörn is saying exactly the same thing I said, re fractional<br>
translations etc...<br>
<br>
In my opiinion, f you want to get exactly zero forces on the atoms that<br>
should have zero forces, monitor them as a function of k-point sampling.<br>
<br>
Ss you increase the k-points, the ground state charge density should<br>
converge to the symmetric one, even if it has not been symmetrized by<br>
hand by the code.<br>
<br>
Also note that 5 5 1 sampling seems to me very inhomogeneous in the<br>
three different directions - why don't you try 2 2 2, 3 3 3, 4 4 4, 8 8 <br>
8, ...<br>
and see how it goes (and maybe report?).<br>
<br>
Thanks a lot,<br>
<br>
nicola<br>
<br>
<br>
<br>
On 30/05/2015 19:03, Manuel Pérez Jigato wrote:<br>
> hi mkondrin<br>
><br>
> the email below, from the author of cif2cell, explains the reasons for<br>
> having<br>
> zero forces for all copper and chromium atoms on the basis of the CIF<br>
> 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<br>
> lines are oxygen, next three lines are Cr, last 3 lines are copper<br>
> atoms), from a low cutoff, small number of k-points abinit calculation<br>
> (in the espresso calculation some copper and chromium atoms are fixed,<br>
> other copper and chromium atoms move, which means some of the<br>
> copper-copper, chromium-copper and chromium-chromium distances vary, and<br>
> theyshould 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<br>
><br>
> -----Forwarded by Manuel Pérez Jigato/LIST on 05/30/2015 06:35PM -----<br>
> 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>
> Well, whether or not it is explicitly used for symmetrization, the<br>
> symmetry is of course still there. So if by symmetry the forces should<br>
> be zero, then they should be zero. In your case I can see from the CIF<br>
> that the forces should indeed be zero, since they are 3a and 3b Wyckoff<br>
> positions, which have no free parameters. If they are not, then there is<br>
> some form of numerical problem, how bad it is of course depends on how<br>
> large the forces are. The manual mentioned that the fourier mesh might<br>
> not having the symmetry of the lattice in all cases, it may be that it<br>
> is possible to get that in order by selecting them as multiples of 3 for<br>
> a trigonal lattice. That's all I can say, I don't know anything specific<br>
> about QE.<br>
><br>
> Cheers,<br>
> Torbjörn<br>
><br>
> ---<br>
> Torbjörn Björkman, PhD<br>
> COMP, Aalto University School of Science<br>
> Espoo, Finland<br>
><br>
> ------------------------------------------------------------------------<br>
> *Från:* Manuel Pérez Jigato [manuel.perez@list.lu]<br>
> *Skickat:* den 29 maj 2015 14:42<br>
> *Till:* Björkman Torbjörn<br>
> *Ämne:* Re: SV: SV: cif2cell enquiry<br>
><br>
> thanks a lot Bjorkman, it is very kind of you<br>
> my only worry would be the possible implications for the forces<br>
> I will ask to the pwscf mailing list<br>
> regards<br>
> Manuel<br>
><br>
> Inactive hide details for Björkman Torbjörn ---29/05/2015<br>
> 12:08:34---Dear Manuel, I can find nothing that looks wrong in the<br>
> ciBjörkman Torbjörn ---29/05/2015 12:08:34---Dear Manuel, I can find<br>
> nothing that looks wrong in the cif2cell output, but a quick look in the "Tr<br>
><br>
> From: Björkman Torbjörn <torbjorn.bjorkman@aalto.fi><br>
> To: Manuel Pérez Jigato <manuel.perez@list.lu>,<br>
> Date: 29/05/2015 12:08<br>
> Subject: SV: SV: cif2cell enquiry<br>
><br>
> ------------------------------------------------------------------------<br>
><br>
><br>
><br>
> Dear Manuel,<br>
><br>
> I can find nothing that looks wrong in the cif2cell output, but a quick<br>
> look in the "Troubleshooting" section of the QE manual seems to provide<br>
> the most likely answer:<br>
><br>
> pw.x does not find all the symmetries you expected<br>
><br>
><br>
> ...<br>
><br>
> * a fractional translation, without rotation, is a symmetry operation<br>
> of the system. This means that the cell is actually a supercell. In<br>
> this case, all symmetry operations containing fractional<br>
> translations are disabled. The reason is that in this rather exotic<br>
> case there is no simple way to select those symmetry operations<br>
> forming a true group, in the mathematical sense of the term.<br>
><br>
><br>
> What they say is that QE in cases like these will just say "this is a<br>
> supercell" and throw the fractional translations away, which gives you<br>
> 12 symmetries instead of 36, just as it should. I have no idea if you<br>
> can bypass this behaviour in QE though, better ask on their mailing list.<br>
><br>
> Hope this helps,<br>
> Torbjörn<br>
><br>
> ---<br>
> Torbjörn Björkman, PhD<br>
> COMP, Aalto University School of Science<br>
> Espoo, Finland<br>
><br>
> ------------------------------------------------------------------------<br>
><br>
> *Från:* Manuel Pérez Jigato [manuel.perez@list.lu]*<br>
> Skickat:* den 29 maj 2015 12:37*<br>
> Till:* Björkman Torbjörn*<br>
> Ämne:* Re: SV: cif2cell enquiry<br>
><br>
> Dear Bjorkman<br>
><br>
> thanks for your prompt reply<br>
> please find enclosed the files/(See attached file: esta.cif)(See<br>
> attached file: QE_NOREDUCE_esta.in)(See attached file: second.in)(See<br>
> attached file: second.out)(See attached file: output_noreduce.txt)/<br>
><br>
> Manuel<br>
> PS the different between the two .in files is that one of them is the<br>
> direct output from cif2cell, whilst the other is produced by<br>
> adding a few options by hand, before running quantum-espresso (whose<br>
> output you can see as well)<br>
><br>
><br>
> _______________________________________________<br>
> Pw_forum mailing list<br>
> Pw_forum@pwscf.org<br>
> </font></tt><tt><font size="2"><a href="http://pwscf.org/mailman/listinfo/pw_forum">http://pwscf.org/mailman/listinfo/pw_forum</a></font></tt><tt><font size="2"><br>
><br>
<br>
-- <br>
<br>
----------------------------------------------------------------------<br>
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL<br>
Director, National Centre for Competence in Research NCCR MARVEL, EPFL<br>
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