[Pw_forum] Fwd: Basic Relax Calculation issues

[Filipe Camargo Dalmatti Alves Lima]

Dear Zarah,

Have you ever considered that you may want the cell relaxation in this
case? (vc-relax)
It will optimize the cell parameter in order to minimize the total energy.
You'll see that the system might have lots of interactions.

If you want to explore defects in crystals or surfaces, relaxing the
internal coordinates are essential since you are breaking the symmetry in
some way: by having impurities; surface interaction; vacancy defects and
etc. If it is the case you want to explore, you will need to use a
supercell approach. Remember: crystals are built based on symmetry rules.

If you are really curious, you might try to change the cell symmetry just
to observe how the internal coordinations behave (just increase z by 0.2).
It may not converge, but you will see a lot interactions.

Best regards,

Filipe

On Friday, February 28, 2014, Zarah Baiyee <z.baiyee at gmail.com> wrote:

> Hi All,
>
> I am a new user to Quantum Espresso, therefore this may be a bit trivial
> but I any help would be very welcome.
>
> I am attempting a relax calculation using espresso version 5.0.2, for the
> geometry optimisation of a perovskite structure. For the input below, the
> calculation runs, however does not compute any forces and convergence
> without geometry optimisation to the original structure, with 0 bfgs steps.
> I am able to perform an expected relaxation if alter the initial atomic
> positions to asymmetric: (i.e.)  an oxygen molecule from:  O (0.500  0.5
>  0.0) to O(0.499 0.5 0.0).
>
> Please may someone shed some light on to why this is the case, and if
> there is anything wrong with my input.
>
> Thanks
>
> Zarah
> Zbaiyee at gmail.com <javascript:_e(%7B%7D,'cvml','Zbaiyee at gmail.com');>
>
> &CONTROL
>   calculation  = "relax",
>   prefix       = "CO",
>   pseudo_dir   = "/Users/zarahbaiyee/espresso-5.0.2/pseudo",
>   outdir       = "/Users/zarahbaiyee/tmp",
>   forc_conv_thr = 1.0D-5
> /
> &SYSTEM
>   ibrav     = 0,
>   nat       = 5,
>   ntyp      = 3,
>   ecutwfc   = 60,
>   ecutrho   = 420,
> /
> &ELECTRONS
>   conv_thr    = 1.D-7,
>   mixing_beta = 0.7D0,
>   electron_maxstep = 400
> /
> &IONS
> /
> CELL_PARAMETERS bohr
>  7.60  0.0  0.0
>  0.0  7.60  0.0
>  0.0  0.0  7.60
> ATOMIC_SPECIES
>  Ba  137.32 Ba.pbe-mt_fhi.UPF
>  Fe  55.84 Fe.pbe-mt_fhi.UPF
>  O   15.99 O.pbe-kjpaw.UPF
> ATOMIC_POSITIONS {crystal}
> Ba  0.000  0.0  0.0  0 0 0
> Fe  0.500  0.5  0.5
> O   0.000  0.5  0.5
> O   0.500  0.0  0.5
> O   0.500  0.5  0.0
> K_POINTS {automatic}
> 9 9 9 0 0 0
>
>

-- 
_________________________________________
Filipe Camargo Dalmatti Alves Lima
PhD Student
University of São Paulo, Physics Institute, Materials Physics Department,
Nanomol Group, Brazil.
Phones:    (11) 3091-6881  (USP)
                (11) 97408-2755 (Vivo)
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