[Pw_forum] relax vs multiple SCF calculations inconsistency

[sarashs]

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