[Pw_forum] about the ibrav=0

[hyello25 Qgrui]

hi,
*  When I use ibrav=0 to calculate the force of Si, I encounter some
problems. Are there some thing wrong in my codes?*

  &system
    ibrav = 0,
      nat = 2,
     ntyp = 1,
     ecutwfc = 50,
        A =   5.39780000 ,
        B =   5.39780000 ,
        C =   5.39780000 ,
        cosAB = 0.500000 ,
        cosAC = 0.500000 ,
        cosBC = 0.500000 ,
 /
 &electrons
    mixing_beta = 0.7
    conv_thr =  1.0d-7
 /
ATOMIC_SPECIES
 Si  28.086  Si.vbc.UPF
ATOMIC_POSITIONS crystal
 Si  0.00000 0.00000 0.00000
 Si  0.25000 0.25000 0.25000
CELL_PARAMETERS cubic
     0.288675135    -0.500000000     0.816496581
     0.288675135     0.500000000     0.816496581
    -0.577350269     0.000000000     0.816496581
K_POINTS automatic
 4 4 4 1 1 1

*  The result is below, why does force exit in this situation?*

!    total energy              =   -15.46091639 ryd
     estimated scf accuracy    <     0.00000003 ryd

     band energy sum           =    -2.48914635 ryd
     one-electron contribution =    -1.72655466 ryd
     hartree contribution      =     2.24142346 ryd
     xc contribution           =    -4.02628209 ryd
     ewald contribution        =   -11.94950310 ryd

     convergence has been achieved

     Forces acting on atoms (Ry/au):

* **    atom   1 type  1   force =     0.00314138    0.00000000   -
0.00856639
     atom   2 type  1   force =    -0.00314138    0.00000000    0.00856639*

     Total force =     0.012904     Total SCF correction =     0.000110


     entering subroutine stress ...

          total   stress  (ryd/bohr**3)                  (kbar)     P=  -
86.51
  -0.00058668   0.00000000   0.00000976        -86.30      0.00      1.44
   0.00000000  -0.00058838   0.00000000          0.00    -86.55      0.00
   0.00000976   0.00000000  -0.00058914          1.44      0.00    -86.67

*Another question :whether we need not ot set cosAB, cosAC, cosBC when we
use ibrav=0?*

  thanks.
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