[Pw_forum] internal position after relax

[Djani Ait Aissa Hania]

dear all,
after the relaxationof my structure, I noticed the position of one oxygens atom along the z-direction became greater than celldm(3) wich is physically impossible. 
celldm(3)=2.992
O(0.2981  0.7355  2.9597) =>after relax O(0.385...  0.781...  3.0147).
What could that mean?
here are  input and output informations. Please don't pay attention to the Warning card in the output, I fix it but the position of that oxygen is still out off 2.299.
 
 /
 &system
    ibrav=9
    celldm(1)=10.45, 
    celldm(2)=0.994, 
    celldm(3)=2.992, 
    nat=18
    ntyp=3
    ecutwfc=35.0
    ecutrho=200.0, 
 /
 &electrons
    conv_thr = 1e-6,
    mixing_beta=0.7,
 /
 &ions
 /
ATOMIC_SPECIES
  
  W     183.84    W.pz-bhs.UPF
  Bi    208.98    083-Bi-ca-d-vgrp_ji.uspp.UPF
  O     15.9994   O.pz-van_ak.UPF
 
ATOMIC_POSITIONS alat
W        0.000000000   0.000000000   0.000000000 0 0 0 
W        0.000000000   0.497000000   1.496000000 0 1 1
Bi       0.994700000   0.508500000   0.515300000
Bi       0.994700000   0.485500000   2.476700000
Bi       0.994700000   0.982500000   2.011300000
Bi       0.994700000   0.011500000   0.980700000
O        0.075300000   0.952900000   0.323100000
O        0.075300000   0.041100000   2.668900000
O        0.075300000   0.538100000   1.819100000
O        0.075300000   0.455900000   1.172900000
O        0.277100000   0.253500000   2.243700000
O        0.277100000   0.740500000   0.748300000
O        0.277100000   0.243500000   0.747700000
O        0.277100000   0.750500000   2.244300000
O        0.298100000   0.735500000   2.959700000
O        0.298100000   0.258500000   0.032300000
O        0.298100000   0.755500000   1.463700000
O        0.298100000   0.238500000   1.528300000

K_POINTS{automatic}
  6 6 2 1 1 1

 
     Program PWSCF     v.3.2.3  starts ...
       Ultrasoft (Vanderbilt) Pseudopotentials

     Current dimensions of program pwscf are:

     ntypx = 10   npk = 40000  lmax =  3
     nchix =  6  ndmx =  2000  nbrx = 14  nqfx =  8
Warning: card K_POINTS{AUTOMATIC} ignored
Warning: card   6 6 2 1 1 1 ignored

     gamma-point specific algorithms are used


     bravais-lattice index     =            9
     lattice parameter (a_0)   =      10.4500  a.u.
     unit-cell volume          =    1696.9414 (a.u.)^3
     number of atoms/cell      =           18
     number of atomic types    =            3
     kinetic-energy cutoff     =      35.0000  Ry
     charge density cutoff     =     200.0000  Ry
     convergence threshold     =      1.0E-06
     beta                      =       0.7000
     number of iterations used =            8  plain     mixing
     Exchange-correlation      =  SLA  PZ   NOGX NOGC (1100)
     nstep                     =           50

     celldm(1)=  10.450000  celldm(2)=   0.994000  celldm(3)=   2.992000
     celldm(4)=   0.000000  celldm(5)=   0.000000  celldm(6)=   0.000000

     crystal axes: (cart. coord. in units of a_0)
               a(1) = (  0.500000  0.497000  0.000000 )  
               a(2) = ( -0.500000  0.497000  0.000000 )  
               a(3) = (  0.000000  0.000000  2.992000 )  

     reciprocal axes: (cart. coord. in units 2 pi/a_0)
               b(1) = (  1.000000  1.006036  0.000000 )  
               b(2) = ( -1.000000  1.006036  0.000000 )  
               b(3) = (  0.000000  0.000000  0.334225 )  

     
     4 Sym.Ops. (no inversion)
   
     entering subroutine stress ...

          total   stress  (Ry/bohr**3)                   (kbar)     P=  219.52
   0.00240206   0.00000000   0.00000000        353.35      0.00      0.00
   0.00000000   0.00197220   0.00000000          0.00    290.12      0.00
   0.00000000   0.00000000   0.00010257          0.00      0.00     15.09


     The maximum number of steps has been reached.

     End of BFGS Geometry Optimization

CELL_PARAMETERS (alat)
   0.500000000   0.497000000   0.000000000
  -0.500000000   0.497000000   0.000000000
   0.000000000   0.000000000   2.992000000

ATOMIC_POSITIONS (alat)
W        0.000000000   0.000000000   0.000000000
W        0.000000000   0.497000000   1.496000000
Bi       0.884736162   0.286360920   0.513309795
Bi       0.884736162   0.707639080   2.478690205
Bi       0.884736162   1.204639080   2.009309795
Bi       0.884736162  -0.210639080   0.982690205
O        0.114341213   0.998396235   0.303938731
O        0.114341213  -0.004396235   2.688061269
O        0.114341213   0.492603765   1.799938731
O        0.114341213   0.501396235   1.192061269
O        0.136327487   0.459631702   2.459832528
O        0.136327487   0.534368298   0.532167472
O        0.136327487   0.037368298   0.963832528
O        0.136327487   0.956631702   2.028167472
O        0.385241009   0.781832443   3.014719481
O        0.385241009   0.212167557  -0.022719481
O        0.385241009   0.709167557   1.518719481
O        0.385241009   0.284832443   1.473280519


      
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