[Pw_forum] Problem in VC-relaxation with fixed atomic positions

[Marcos Veríssimo Alves]

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 Veríssimo 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 Física La Plata
> >> La Plata - Argentina
> >>
> >>
> >> 2014-06-05 21:40 GMT-03:00 Marcos Veríssimo 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://lists.quantum-espresso.org/pipermail/users/attachments/20140606/d8557cfd/attachment.html>