[QE-users] GET BUCKLING IN OPTIMIZATION

[Barsha Pal]

Hello everyone,
I am trying to optimize a structure existing in literature. It is reported
to have buckling not planar. I made the pristine (only carbon -- totally
planar) analogue of the structure and doped it to my target. Now on
optimizing the z coordinates do not change at all. I need the z to be
changed as well to get the target buckling. Also the optimization converged
for a loose criteria
( energy convergence thresh.=  1.0E-05
     force convergence thresh. =      1.0E-04
     press convergence thresh. =      5.0E-03)
and when I tighten the criteria, BFGS fails. I have tried optimizing with
and without cell_dofree = all and 2Dxy, but the z remains unchanged.


The input specifications are:

&CONTROL
    calculation   = "vc-relax"
    restart_mode  = "from_scratch"
    outdir  = "/tmp/"
    prefix  = "pwscf"
    pseudo_dir  = "/p/"
    verbosity     = "high"
    etot_conv_thr = 1.0D-6
    forc_conv_thr = 1.0D-5
    nstep  = 1000
    tprnfor  = .true.
    disk_io  = "none"
/

&SYSTEM
  ibrav     = 0
  celldm(1)  = 14.629678225
  nat        = 8
  ntyp       = 2
  ecutwfc    = 170
  ecutrho    = 680
  occupations = "smearing"
  smearing = "mv"
  degauss = 0.005

/

&ELECTRONS
    electron_maxstep = 600
    mixing_beta = 0.3
    conv_thr =  1.0d-6
/

&IONS
    ion_dynamics = "bfgs"
/

&CELL
    press   =  0.0
    cell_dynamics  = "bfgs"
    cell_dofree   = "2Dxy"
/

ATOMIC_SPECIES
A   000  A.pbe-dnl-kjpaw_psl.1.0.0.UPF
 B  00  B.pbe-nl-kjpaw_psl.1.0.0.UPF

CELL_PARAMETERS (alat=  14.629678225 )
   1.000000000   0.000000000   0.000000000
   0.000000000   1.000000000   0.000000000
   0.000000000   0.000000000   2.583596722

ATOMIC_POSITIONS (crystal)
A              0.6470402285        0.1471007113        0.5000000000
B                0.6491194122        0.8509186097        0.5000000000
B               0.3508805878        0.1490813903        0.5000000000
A              0.3529597715        0.8528992887        0.5000000000
A             0.1471007113        0.3529597715        0.5000000000
B                0.8509186097        0.3508805878        0.5000000000
B                0.1490813903        0.6491194122        0.5000000000
A             0.8528992887        0.6470402285        0.5000000000

K_POINTS {automatic}
  12 12 3 0 0 0


NOTE: This is supposed to be a 2D surface with buckling and with a band gap.


Ashley Cooper
Phd
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