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

[N. Plugaru]

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> 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:_e(%7B%7D,'cvml','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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