Thanks, Nucu. That might be the reason. I suppose that, if I want to have fixed cartesian coordinates, I'd have to dig into the code. i wonder if the developers could give me a hint of where to change the code. It would, in principle, be a simple matter: change the coordinates so that the cartesian ones would remain the same, but would there be any caveats to that in the context of variable-cell calculations?<div>
<br></div><div>Best regards,</div><div><br></div><div>Marcos<br><br>On Friday, June 6, 2014, N. Plugaru <<a href="mailto:plug@infim.ro">plug@infim.ro</a>> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Dear Marcos<br>
<br>
Please, see this link, it is explanatory for vc-relax :<br>
<br>
<a href="http://qe-forge.org/pipermail/pw_forum/2014-March/103393.html" target="_blank">http://qe-forge.org/pipermail/pw_forum/2014-March/103393.html</a><br>
<br>
Best regards,<br>
Nucu<br>
<br>
On Fri, June 6, 2014 7:21 am, Marcos VerÃssimo Alves wrote:<br>
> Thanks, Arles, but I opened the relaxation on xcrysden and on the first<br>
> step the cell was hexagonal.<br>
><br>
> Best,<br>
><br>
> Marcos<br>
><br>
> On Thursday, June 5, 2014, Arles V. Gil Rebaza <<a href="javascript:;" onclick="_e(event, 'cvml', 'arvifis@gmail.com')">arvifis@gmail.com</a>> wrote:<br>
><br>
>> Dear Marcos, please review your CELL_PARAMETERS tag..!! I thing that<br>
>> there<br>
>> are some mistakes... you are using a square 2D lattice and not a<br>
>> hexagonal<br>
>> one.<br>
>><br>
>> Best<br>
>><br>
>> PhD. Arles V. Gil Rebaza<br>
>> Instituto de FÃsica La Plata<br>
>> La Plata - Argentina<br>
>><br>
>><br>
>> 2014-06-05 21:40 GMT-03:00 Marcos VerÃssimo Alves <<br>
>> <a href="javascript:;" onclick="_e(event, 'cvml', 'marcos.verissimo.alves@gmail.com')">marcos.verissimo.alves@gmail.com</a><br>
>> <javascript:_e(%7B%7D,'cvml','<a href="javascript:;" onclick="_e(event, 'cvml', 'marcos.verissimo.alves@gmail.com')">marcos.verissimo.alves@gmail.com</a>');>>:<br>
>><br>
>>> Hi all,<br>
>>><br>
>>> I am trying to perform a cell optimization for graphene in which I<br>
>>> would<br>
>>> like to fix the atomic positions so as to have arbitrary bond lengths,<br>
>>> and<br>
>>> see what happens to the in-plane cell vectors. Thus I would like to<br>
>>> keep<br>
>>> the atomic positions fixed and let the in-plane cell vectors change.<br>
>>><br>
>>> I am using vc-relax with cell_dofree="2dxy" and I am (theoretically)<br>
>>> fixing atomic positions (specified in Angstrom) with "0 0 0" after the<br>
>>> cartesian coordinates. The problem is, the coordinates do not remain<br>
>>> fixed<br>
>>> during the cell optimization:<br>
>>><br>
>>> ATOMIC_POSITIONS (angstrom)<br>
>>> C 0.000000000 0.000000000 7.000000000 0 0 0<br>
>>> C 1.508583432 0.000000000 7.000000000 0 0 0<br>
>>> --<br>
>>> ATOMIC_POSITIONS (angstrom)<br>
>>> C 0.000000000 0.000000000 7.000000000 0 0 0<br>
>>> C 1.553137965 0.000000000 7.000000000 0 0 0<br>
>>> --<br>
>>> ATOMIC_POSITIONS (angstrom)<br>
>>> C 0.000000000 0.000000000 7.000000000 0 0 0<br>
>>> C 1.583982256 0.000000000 7.000000000 0 0 0<br>
>>> --<br>
>>> ATOMIC_POSITIONS (angstrom)<br>
>>> C 0.000000000 0.000000000 7.000000000 0 0 0<br>
>>> C 1.592677072 0.000000000 7.000000000 0 0 0<br>
>>> --<br>
>>> ATOMIC_POSITIONS (angstrom)<br>
>>> C 0.000000000 0.000000000 7.000000000 0 0 0<br>
>>> C 1.597484048 0.000000000 7.000000000 0 0 0<br>
>>> --<br>
>>> ATOMIC_POSITIONS (angstrom)<br>
>>> C 0.000000000 0.000000000 7.000000000 0 0 0<br>
>>> C 1.599092143 0.000000000 7.000000000 0 0 0<br>
>>> --<br>
>>> ATOMIC_POSITIONS (angstrom)<br>
>>> C 0.000000000 0.000000000 7.000000000 0 0 0<br>
>>> C 1.598936919 0.000000000 7.000000000 0 0 0<br>
>>> --<br>
>>> ATOMIC_POSITIONS (angstrom)<br>
>>> C 0.000000000 0.000000000 7.000000000 0 0 0<br>
>>> C 1.598936919 0.000000000 7.000000000 0 0 0<br>
>>><br>
>>> My input is as follows:<br>
>>><br>
>>> &control<br>
>>> calculation='vc-relax'<br>
>>> restart_mode='from_scratch',<br>
>>> prefix='graphene',<br>
>>> pseudo_dir = '/home/mverissi/pseudos_espresso',<br>
>>> outdir='./'<br>
>>> /<br>
>>> &system<br>
>>> ibrav=0,<br>
>>> celldm(1)=4.073139044,<br>
>>> nat=2,<br>
>>> ntyp=1,<br>
>>> nspin = 1,<br>
>>> ecutwfc = 28.0,<br>
>>> ecutrho = 252.0,<br>
>>> occupations='smearing',<br>
>>> smearing='methfessel-paxton',<br>
>>> degauss=0.001,<br>
>>> nbnd=10,<br>
>>> /<br>
>>> &electrons<br>
>>> conv_thr = 1.0e-9,<br>
>>> mixing_beta = 0.7<br>
>>> /<br>
>>> &ions<br>
>>> ion_dynamics='bfgs'<br>
>>> /<br>
>>> &cell<br>
>>> cell_dynamics = 'bfgs',<br>
>>> cell_dofree = '2Dxy',<br>
>>> /<br>
>>> ATOMIC_SPECIES<br>
>>> C 12.0107 C.pbe-rrkjus.UPF<br>
>>> ATOMIC_POSITIONS {angstrom}<br>
>>> C 0.0 >>> <a href="javascript:;" onclick="_e(event, 'cvml', 'Pw_forum@pwscf.org')">Pw_forum@pwscf.org</a> <javascript:_e(%7B%7D,'cvml','<a href="javascript:;" onclick="_e(event, 'cvml', 'Pw_forum@pwscf.org')">Pw_forum@pwscf.org</a>');><br>
>>> <a href="http://pwscf.org/mailman/listinfo/pw_forum" target="_blank">http://pwscf.org/mailman/listinfo/pw_forum</a><br>
>>><br>
>><br>
>><br>
>><br>
>> --<br>
>> ###---------> Arles V. <---------###<br>
>><br>
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