[Pw_forum] relax vs multiple SCF calculations inconsistency

[sarashs]

Hi,

Thanks a lot for your reply. I'll give it a try with constraints but I'm 
also wondering should the other SCF's not have higher energy than the 
equilibrium angle regardless of them being optimized with a constraint? 
I mean if the structure is originally relax (which it is) then one 
expects other near equilibrium structures to have higher energies. Am I 
wrong there?

Regards,

Arash

On 2017-04-17 20:49, Marton wrote:
> 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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