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?
Best regards, Marcos On Friday, June 6, 2014, N. Plugaru <plug at infim.ro> wrote: > Dear Marcos > > Please, see this link, it is explanatory for vc-relax : > > http://qe-forge.org/pipermail/pw_forum/2014-March/103393.html > > Best regards, > Nucu > > On Fri, June 6, 2014 7:21 am, Marcos Ver??ssimo Alves wrote: > > Thanks, Arles, but I opened the relaxation on xcrysden and on the first > > step the cell was hexagonal. > > > > Best, > > > > Marcos > > > > On Thursday, June 5, 2014, Arles V. Gil Rebaza <arvifis at gmail.com > <javascript:;>> wrote: > > > >> Dear Marcos, please review your CELL_PARAMETERS tag..!! I thing that > >> there > >> are some mistakes... you are using a square 2D lattice and not a > >> hexagonal > >> one. > >> > >> Best > >> > >> PhD. Arles V. Gil Rebaza > >> Instituto de F??sica La Plata > >> La Plata - Argentina > >> > >> > >> 2014-06-05 21:40 GMT-03:00 Marcos Ver??ssimo Alves < > >> marcos.verissimo.alves at gmail.com <javascript:;> > >> <javascript:_e(%7B%7D,'cvml','marcos.verissimo.alves at gmail.com > <javascript:;>');>>: > >> > >>> Hi all, > >>> > >>> I am trying to perform a cell optimization for graphene in which I > >>> would > >>> like to fix the atomic positions so as to have arbitrary bond lengths, > >>> and > >>> see what happens to the in-plane cell vectors. Thus I would like to > >>> keep > >>> the atomic positions fixed and let the in-plane cell vectors change. > >>> > >>> I am using vc-relax with cell_dofree="2dxy" and I am (theoretically) > >>> fixing atomic positions (specified in Angstrom) with "0 0 0" after the > >>> cartesian coordinates. The problem is, the coordinates do not remain > >>> fixed > >>> during the cell optimization: > >>> > >>> ATOMIC_POSITIONS (angstrom) > >>> C 0.000000000 0.000000000 7.000000000 0 0 0 > >>> C 1.508583432 0.000000000 7.000000000 0 0 0 > >>> -- > >>> ATOMIC_POSITIONS (angstrom) > >>> C 0.000000000 0.000000000 7.000000000 0 0 0 > >>> C 1.553137965 0.000000000 7.000000000 0 0 0 > >>> -- > >>> ATOMIC_POSITIONS (angstrom) > >>> C 0.000000000 0.000000000 7.000000000 0 0 0 > >>> C 1.583982256 0.000000000 7.000000000 0 0 0 > >>> -- > >>> ATOMIC_POSITIONS (angstrom) > >>> C 0.000000000 0.000000000 7.000000000 0 0 0 > >>> C 1.592677072 0.000000000 7.000000000 0 0 0 > >>> -- > >>> ATOMIC_POSITIONS (angstrom) > >>> C 0.000000000 0.000000000 7.000000000 0 0 0 > >>> C 1.597484048 0.000000000 7.000000000 0 0 0 > >>> -- > >>> ATOMIC_POSITIONS (angstrom) > >>> C 0.000000000 0.000000000 7.000000000 0 0 0 > >>> C 1.599092143 0.000000000 7.000000000 0 0 0 > >>> -- > >>> ATOMIC_POSITIONS (angstrom) > >>> C 0.000000000 0.000000000 7.000000000 0 0 0 > >>> C 1.598936919 0.000000000 7.000000000 0 0 0 > >>> -- > >>> ATOMIC_POSITIONS (angstrom) > >>> C 0.000000000 0.000000000 7.000000000 0 0 0 > >>> C 1.598936919 0.000000000 7.000000000 0 0 0 > >>> > >>> My input is as follows: > >>> > >>> &control > >>> calculation='vc-relax' > >>> restart_mode='from_scratch', > >>> prefix='graphene', > >>> pseudo_dir = '/home/mverissi/pseudos_espresso', > >>> outdir='./' > >>> / > >>> &system > >>> ibrav=0, > >>> celldm(1)=4.073139044, > >>> nat=2, > >>> ntyp=1, > >>> nspin = 1, > >>> ecutwfc = 28.0, > >>> ecutrho = 252.0, > >>> occupations='smearing', > >>> smearing='methfessel-paxton', > >>> degauss=0.001, > >>> nbnd=10, > >>> / > >>> &electrons > >>> conv_thr = 1.0e-9, > >>> mixing_beta = 0.7 > >>> / > >>> &ions > >>> ion_dynamics='bfgs' > >>> / > >>> &cell > >>> cell_dynamics = 'bfgs', > >>> cell_dofree = '2Dxy', > >>> / > >>> ATOMIC_SPECIES > >>> C 12.0107 C.pbe-rrkjus.UPF > >>> ATOMIC_POSITIONS {angstrom} > >>> C 0.0 >>> Pw_forum at pwscf.org <javascript:;> > <javascript:_e(%7B%7D,'cvml','Pw_forum at pwscf.org <javascript:;>');> > >>> http://pwscf.org/mailman/listinfo/pw_forum > >>> > >> > >> > >> > >> -- > >> ###---------> Arles V. <---------### > >> > > _______________________________________________ > > Pw_forum mailing list > > Pw_forum at pwscf.org <javascript:;> > > http://pwscf.org/mailman/listinfo/pw_forum > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org <javascript:;> > http://pwscf.org/mailman/listinfo/pw_forum > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20140606/d8557cfd/attachment.html
