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

[Marcos Veríssimo Alves]

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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