[Pw_forum] How can vc-relax nanosheet that will fall apart or would be bulk?

[khadije alvani]

Dear Q-E users,
I try to  get vc-relax with setting ( using q-e 6.1):

&CONTROL
                 calculation = 'vc-relax' ,
                restart_mode = 'from_scratch' ,
                etot_conv_thr = 1.0E-5  ,
               forc_conv_thr = 1.0D-4 ,
               outdir=
                pseudo_dir =
                tprnfor   = .true.
                tstress = .true.
 /
 &SYSTEM
                        ibrav = 4,
                   celldm(1)=7.3509958804,
                   celldm(3)=3.8560411311,
                     nbnd =16,
                         nat =2,
                        ntyp = 2,
                     ecutwfc = 185 ,
                     ecutrho = 740,
 /
 &ELECTRONS
          conv_thr = 1.D-8 ,
                  electron_maxstep = 5000
                  mixing_beta = 0.7,
/
&IONS
                  ion_dynamics= 'bfgs',
                  upscale  = 100.d0,


/
 &CELL
   cell_dynamics = 'bfgs' ,
   cell_factor = 2
  /
ATOMIC_SPECIES
Zn    65.380    Zn.pbe-d-hgh.UPF
S    32.065    S.pbe-hgh.UPF
ATOMIC_POSITIONS (angstrom)
Zn    0.0    2.248    7.5
S    1.9468251077    1.124    7.5
K_POINTS {automatic}
8 8 1   0 0 0

but when I set  'Z=7.5 ‘ and ' cell _dofree=2Dxy ‘,  the structure of the
nano sheet fell apart and when I relax in 3 directions , Z direction is
decreased and would be bulk structure, so the nano sheet structure will
lose.
Of course it has already been done with gasp,win2k,.. .

I will sincerely appreciate any comment that can help me proceed with my
calculations.
thank you.
with regards
khadije alvani
student of university of IRAN.
tel:  +98  916 813 4896
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