[Pw_forum] relax vs multiple SCF calculations inconsistency

[Marton]

Hi S. Arash Sheikholeslam,

I'm not sure this is the problem but from what you described my
understanding is that when you scan that angle manually you don't optimize
the other degrees of freedom. On the other hand, when you relax the
molecule, all degrees of freedom are relaxed. This discrepancy between the
two approaches could explain the behavior you are seeing. If you are
interested in doing the manual optimization, you could try to relax the
molecule with a constraint on the angle with card CONSTRAINTS.

HTH
Marton Voros

--
Materials Science Division
Argonne National Laboratory


On Mon, Apr 17, 2017 at 8:55 PM, sarashs <sarashs at ece.ubc.ca> wrote:

> Hi,
>
> I've posted this question before but wasn't successful in getting an
> answer. I have a molecule ((OH)3ZrOSi(OH)3) and I want to find the
> equilibrium angle of ZrOSi. The equilibrium angle that I get with a
> "relax" calculation differs a lot from the result I get by increasing
> the angle and performing an "SCF" calculation. I tried various things
> including increasing the ecutwfc and ecutrho and fixing the number of
> bands for both calculations but had no success. Is there any chance
> someone can tell me what I'm missing?
>
> Here's a sample code my code:
>
> &CONTROL
>     calculation = "scf",
>     outdir       = "outputs",
>     prefix     ="ZrSi3",
>     restart_mode="from_scratch"
>     pseudo_dir = "pseudos",
> /
> &SYSTEM
>     nosym       = .TRUE.,
>     ibrav       = 0,
>     nat         = 15,
>     ntyp        = 4,
>     ecutwfc     = 600,
>     ecutrho = 6000,
>     vdw_corr    = "grimme-d2",
> /
> &ELECTRONS
>     conv_thr    = 1.D-11,
>     mixing_beta = 0.5D0,
> /
> ATOMIC_SPECIES
> O   15.9994 O.pz-mt.UPF
> H   1.00794 H.pz-vbc.UPF
> Si  28.0855 Si.pz-vbc.UPF
> Zr  91.224 Zr.pz-hgh.UPF
> ATOMIC_POSITIONS { angstrom }
> H       -0.217652040   2.144165004  -0.967842103
> O       -0.644926428   1.299751587  -1.173517450
> H       -0.763682000  -2.102234442  -0.637701677
> O       -0.631971073  -1.266428593  -1.106959840
> H       -2.244617658   0.059203828   1.041286276
> O       -1.287708239   0.028876445   1.183017241
> Si      -0.341076411   0.043743634  -0.163179170
> O        1.183131599   0.097692502   0.401792709
> Zr       2.959296806   0.743741575   0.268340451
> H        3.161927401   3.483669731   0.077078720
> O        2.777805281   2.601338899   0.023924414
> H        4.228044154   0.110551898   2.670358608
> O        4.003457303   0.315517992   1.757071324
> H        3.597999032  -0.225640653  -2.168546302
> O        3.766434111  -0.029092443  -1.238766538
> K_POINTS { gamma }
> CELL_PARAMETERS { angstrom }
> 13 0 0
> 0 13 0
> 0 0 13
>
> Regards,
>
> S. Arash Sheikholeslam
> PhD candidate at electrical engineering department, University of
> British columbia
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