[Pw_forum] problem with relax convergence in SnO2(110) surface calculation

[Victor Meng'wa]

Dear QE users,
am trying to relax  3 layer SnO2 (110) surface  supercell of 52 atoms but
the calculation does  not converge .i've tried this for the last 3 weeks
but unsuccesful. varied several parameters in the input file but the
problem persists.
i experienced an error
from checkallsym : error #         1
     some of the original symmetry operations not satisfied
but included nosym=.true. the problem didn't recur but still no convergence
The bottom atoms are fixed.
my kpoints and ecut are reduced to ensure fast convergence, once the
problem is fixed i will adjust them.
here is the input file
please welcome any assistance on this.
&CONTROL


restart_mode='from_scratch',


calculation='relax',

     outdir='./',
     pseudo_dir='/home/mikeat/Applications/espresso-4.3.2/pseudo/',
     prefix = 'SnOru_exc1',
     tstress = .t.,
     tprnfor = .t.,
     etot_conv_thr = 1.d-5,
     forc_conv_thr = 1.d-4
     verbosity = 'high'

/
&SYSTEM
     ibrav=6, celldm(1)=44.7607,
     celldm(3)=0.5084,
     nat=  52, ntyp= 2,
     ecutwfc =10,ecutrho = 120,
     occupations='smearing', smearing='marzari-vanderbilt', degauss=0.07
     nosym = .true.
/
&ELECTRONS
      diagonalization = 'david'
      mixing_mode = 'local-TF',
      mixing_beta = 0.3,
      conv_thr = 1.0e-8,
/
&IONS

/
ATOMIC_SPECIES
  Sn 50.011
Sn.pw91-n-van.UPF

 O 15.9994 O.pw91-
van_ak.UPF

ATOMIC_POSITIONS
{bohr}

Sn       8.952203138   26.85642044   -0.000000000
Sn       8.952203138   26.85642044    6.021425723
Sn       17.90421730   26.85642044   -0.000000000
Sn       17.90421730   26.85642044    6.021425723
Sn       13.42821022   22.38041336    3.010712862
Sn       13.42821022   22.38041336    9.032138585
Sn       8.952203138   35.80862358    -0.000000000
Sn       8.952203138   35.80862358    6.021425723
Sn       17.90421730   35.80862358    -0.000000000  0  0  0
Sn       17.90421730   35.80862358     6.021425723  0  0  0
Sn       4.476007083   31.33242752     3.010712862
Sn       4.476007083   31.33242752     9.032138585
Sn       13.42821022   31.33242752     3.010712862
Sn       13.42821022   31.33242752     9.032138585
Sn       22.38041336   31.33242752     3.010712862  0  0  0
Sn       22.38041336   31.33242752     9.032138585  0  0  0
Sn       13.42821022   40.28463066     3.010712862  0  0  0
Sn       13.42821022   40.28463066     9.032138585  0  0  0
O        11.70043294   29.60483921    -0.000000000
O        11.70043294   29.60483921     6.021425723
O        20.65263607   29.60483921     -0.000000000  0  0  0
O       15.155987510   24.10819064     -0.000000000  0  0  0
O        20.65263607   29.60483921     6.021425723   0  0  0
O        15.155987510  24.10819064     6.021425723   0  0  0
O        10.67998042   25.12864316     3.010712862
O        7.224425854   28.58419773     3.010712862
O        7.224425854   28.58419773     9.032138585
O        10.67998042   25.12864316     9.032138585
O        16.17644002   28.58419773     3.010712862
O        16.17644002   28.58419773     9.032138585
O        11.70043294   38.55685338     -0.000000000
O        6.203784367   33.06020481     -0.000000000
O        11.70043294   38.55685338     6.021425723
O        6.203784367   33.06020481     6.021425723
O        15.155987510  33.06020481     -0.000000000
O        15.155987510  33.06020481      6.021425723
O        10.679980420  34.0808463       3.010712862
O        10.679980420  34.0808463       9.032138585
O        19.631994590  34.0808463       3.010712862
O        19.631994590  34.0808463        9.032138585
O        16.176440020  37.53640086      3.010712862
O        16.176440020  37.53640086      9.032138585
Sn       8.952203138   26.85642044      12.04285145
Sn       17.90421730   26.85642044      12.04285145
Sn       8.952203138   35.80862358      12.04285145
Sn       17.90421730   35.80862358      12.04285145  0  0  0
O        11.70043294   29.60483921      12.04285145
O        20.65263607   29.60483921       12.04285145 0  0  0
O        15.15598751   24.10819064      12.04285145  0  0  0
O        11.70043294   38.55685338      12.04285145
O        6.203784367   33.06020481      12.04285145
O        15.15598751   33.06020481      12.04285145

K_POINTS {automatic}

  2 2 3  0 0 0


VICTOR KIRUI MENG'WA,MSC STUDENT
CHEPKOILEL UNIVERSITY COLLEGE,
COMPUTATIONAL PHYSICS GROUP,
ELDORET, KENYA
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