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

[Arles V. Gil Rebaza]

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>:

> 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     0.0   7.0    0  0  0
> C    1.42    0.0   7.0    0  0  0
> K_POINTS {automatic}
>        24   24   1  0  0  0
> CELL_PARAMETERS {alat}
>    0.866025404   0.5  0.0
>    0.866025404  -0.5  0.0
>    0.000000000   0.0  6.0
>
> Am I making some silly mistake here? The version of Espresso in use is
> 5.0.2. Sorry if this has already come up, but I couldn't find anything
> similar to my problem.
>
> Best regards,
>
> Marcos
>
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-- 
###--------->   Arles V.   <---------###
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