[Pw_forum] relaxation with vc-relax

[Payam Norouzzadeh]

Dear QE users

My system has 54 atoms with a BCC structure. Its primitive unit cell
includes 27 atoms.
I am trying to find its lattice constant by using vc-relax.
After running it several times and for more than 3 weeks still the
convergence thresholds are not satisfied.
The forces don't like to get smaller than a specific value (around 0.02).
Is something wrong with my input file? Please let me know your comments.

Best regards,Payam Norouzzadeh


&CONTROL
  title = Eight,
  calculation  = "vc-relax",
  restart_mode = 'from_scratch' ,
  prefix       = "Eight",
  pseudo_dir   = "/...",
  wfcdir = '...' ,
  outdir = '/...',
  nstep =  100  ,
  etot_conv_thr = 1.0E-9  ,
  forc_conv_thr = 5.0D-5 ,
  max_seconds = 172800 ,
  dt = 100 ,
/
&SYSTEM
  ibrav = 3,
  celldm(1)=19.622,
  nat  = 27,
  ntyp = 3,
  ecutwfc   = 70.D0,
  ecutrho   = 700.D0,
  occupations='smearing',
  smearing='gaussian',
  degauss=0.02,
/
&ELECTRONS
diagonalization = 'cg',
  conv_thr    = 1.D-9,
  mixing_beta = 0.5D0,
/
&IONS
 ion_dynamics = 'damp' ,
/
&CELL
cell_dynamics = 'damp-w',
/
ATOMIC_SPECIES
Al   26.98154  Al.pw91-n-van.UPF
Si   28.0855   Si.pw91-n-van.UPF
Ba   137.327   Ba.pw91-nsp-van.UPF
ATOMIC_POSITIONS crystal
Al       0.216201457   0.378180997   0.237078143
Al       0.034697037   0.023737131   0.761262755
Al       0.547173316   0.281036341   0.747383956
Al       0.499243974   0.592176706   0.241711510
Al       0.079436185   0.571961647   0.770077147
Al       0.696760320   0.247074460   0.186155320
Al       0.763858042   0.534829188   0.108400015
Si      -0.084375501   0.661831874  -0.052015722
Si       0.768579606   0.003812573   0.065138231
Si       0.015665804  -0.146726664   0.029763195
Si       0.219167074   0.647981279   0.510896217
Si       0.688206047   0.299356062   0.551238353
Si       0.813578233   0.574824765   0.373099840
Si       0.455287149   0.559729400   0.815079368
Si       0.236709112   0.370770979   0.535759218
Si      -0.101920499   0.795055135   0.400098065
Si       0.540358072   0.119760142   0.526376973
Si       0.817782198   0.005623765   0.511008919
Si       0.260966498   0.808368895   0.269851937
Si       0.611991634  -0.079635051   0.839306911
Si       0.368449934   0.463356223   0.046445257
Si       0.051075029   0.331552898   0.665912314
Si       0.416741872   0.793935246  -0.103728118
Ba       0.635745128   0.714712066   0.579828902
Ba       0.158096139   0.054209356   0.465675155
Ba      -0.077117796   0.267386792  -0.044545628
Ba       0.416141346   0.060760806   0.081304511
K_POINTS automatic
6 6 6  0 0 0
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