[Pw_forum] vc-relax : total force does not converge

Jiseok Kim tube77 at gmail.com
Wed Sep 5 01:04:39 CEST 2012


Dear QE users,

I'm having a difficulty on a geometry optimization using 'vc-relax'.
I searched forum threads and followed various suggestions but the 'Total
force' still does not converge..
(but the pressures seems to be converged)

The job steps I've taken as follows,

1. optimized k-point and ecutwfc.
2. optimized lattice parameter using Murnaghan fitting.
3. 'relax' the geometry using the lattice constant obtained from step2,

----------------------------------------------
&control
  calculation     = 'relax',
  restart_mode    = 'from_scratch',
  prefix          = '$NAME',
  pseudo_dir      = '$PSEUDO_DIR/',
  outdir          = '$OUT_DIR/',
  wf_collect      = .TRUE.
  tstress         = .TRUE.
  tprnfor         = .TRUE.
  etot_conv_thr   = 1.d-7
  forc_conv_thr   = 1.d-6
  nstep           = 1000
/
&system
  ibrav           = 0,
  celldm(1)       = 10.3345
  nat             = 18,
  ntyp            = 2,
  ecutwfc         = 80.0,
/
&electrons
  diagonalization = 'cg',
  mixing_mode     = 'plain',
  mixing_beta     = 0.7,
  conv_thr        = 1.0d-10,
/
&ions
  ion_dynamics    = 'bfgs'
  bfgs_ndim       = 3
/
ATOMIC_SPECIES
Si 28.086  Si.pbe-rrkj.UPF
H  1.0079  H.pbe-vbc.UPF
CELL_PARAMETERS
     4.89897948556636    0.00000000000000    0.00000000000000
     0.00000000000000    5.19615242270663    0.00000000000000
     0.00000000000000    0.00000000000000    0.70710678118655
ATOMIC_POSITIONS angstrom
Si           6.65158939652772    10.19066526389879     0.00000000000000
Si           7.76018762928234     9.40676793590657     1.92014846431207
Si           9.97738409479158    10.19066526389879     1.92014846431207
Si          11.08598232754620     9.40676793590657     0.00000000000000
Si          13.30317879305544    10.19066526389879     0.00000000000000
Si          14.41177702581006     9.40676793590657     1.92014846431207
Si          16.62897349131930    10.19066526389879     1.92014846431207
Si          17.73757172407392     9.40676793590657     0.00000000000000
H            6.65158939652772    11.67767298594874     0.00000000000000
H            7.76018762928234     7.91976021385662     1.92014846431207
H            9.97738409479158    11.67767298594874     1.92014846431207
H           11.08598232754620     7.91976021385662     0.00000000000000
H           13.30317879305544    11.67767298594874     0.00000000000000
H           14.41177702581006     7.91976021385662     1.92014846431207
H           16.62897349131930    11.67767298594874     1.92014846431207
H           17.73757172407392     7.91976021385662     0.00000000000000
H            5.24962507127668     9.69499602321547     0.00000000000000
H           19.13953604932496     9.90243717658989     0.00000000000000
K_POINTS automatic
1 1 16 0 0 0 
----------------------------------------------


4. check if 'Total force' is converged -> OK.
5. Take the final atomic coordinates from step4.
6. Run 'vc-relax' as,

----------------------------------------------
&control
  calculation     = 'vc-relax',
  restart_mode    = 'from_scratch',
  prefix          = '$NAME',
  pseudo_dir      = '$PSEUDO_DIR/',
  outdir          = '$OUT_DIR/',
  wf_collect      = .TRUE.
  tstress         = .TRUE.
  tprnfor         = .TRUE.
  etot_conv_thr   = 1.d-6
  forc_conv_thr   = 1.d-6
  nstep           = 10000
/
&system
  ibrav           = 0,
  celldm(1)       = 10.3345
  nat             = 18,
  ntyp            = 2,
  ecutwfc         = 80.0,
  ecfixed         = 70.0,
  qcutz           = 150.0,
  q2sigma         = 4.0,
/
&electrons
  diagonalization = 'cg',
  mixing_mode     = 'plain',
  mixing_beta     = 0.7,
  conv_thr        = 1.0d-10,
/
&ions
  ion_dynamics    = 'bfgs'
  bfgs_ndim       = 3
/
&cell
  cell_dynamics   = 'bfgs'
  press_conv_thr  = 0.1d0
  press           = 0.d0
  cell_factor     = 2.d0
/
ATOMIC_SPECIES
Si 28.086  Si.pbe-rrkj.UPF
H  1.0079  H.pbe-vbc.UPF
CELL_PARAMETERS
     4.89897948556636    0.00000000000000    0.00000000000000
     0.00000000000000    5.19615242270663    0.00000000000000
     0.00000000000000    0.00000000000000    0.70710678118655
ATOMIC_POSITIONS angstrom
Si       6.595371055  10.174313717  -0.005918138
Si       7.697686348   9.425353751   1.927575025
Si       9.940638827  10.152944754   1.927571298
Si      11.073523827   9.431959516  -0.005942277
Si      13.315586210  10.165270258  -0.005944217
Si      14.448496999   9.444343582   1.927568680
Si      16.691414457  10.172072841   1.927571881
Si      17.793848036   9.423269303  -0.005921592
H        6.597479872  11.672720999  -0.006012302
H        7.704912055   7.923796337   1.927472273
H        9.942740551  11.655007902   1.927566837
H       11.078852672   7.930134628  -0.005961188
H       13.310208995  11.667097994  -0.005963695
H       14.446478909   7.942288221   1.927563469
H       16.684085788  11.673634035   1.927468080
H       17.791980426   7.924865718  -0.006016781
H        5.166205416   9.718188689  -0.005743345
H       19.222939638   9.879636554  -0.005746296
K_POINTS automatic
1 1 16 0 0 0 
----------------------------------------------



Then the output 'Total force' seems to oscillates and does not converge as
shown below,



----------------------------------------------------------------------------
-------------
     Total force =     0.000723     Total SCF correction =     0.000009
     Total force =     0.000288     Total SCF correction =     0.000010
     Total force =     0.000172     Total SCF correction =     0.000001
     Total force =     0.000227     Total SCF correction =     0.000005
     Total force =     0.000323     Total SCF correction =     0.000005
     Total force =     0.000327     Total SCF correction =     0.000004
     Total force =     0.000393     Total SCF correction =     0.000004
     Total force =     0.000682     Total SCF correction =     0.000004
     Total force =     0.000811     Total SCF correction =     0.000006
     Total force =     0.000803     Total SCF correction =     0.000007
     Total force =     0.000427     Total SCF correction =     0.000001
     Total force =     0.000392     Total SCF correction =     0.000002
     Total force =     0.000380     Total SCF correction =     0.000001
     Total force =     0.000233     Total SCF correction =     0.000001
     Total force =     0.000164     Total SCF correction =     0.000001
     Total force =     0.000227     Total SCF correction =     0.000001
     Total force =     0.000246     Total SCF correction =     0.000000
     Total force =     0.000299     Total SCF correction =     0.000001
     Total force =     0.000320     Total SCF correction =     0.000001
     Total force =     0.000230     Total SCF correction =     0.000001
     Total force =     0.000129     Total SCF correction =     0.000001
     Total force =     0.000147     Total SCF correction =     0.000000
     Total force =     0.000131     Total SCF correction =     0.000001
     Total force =     0.000104     Total SCF correction =     0.000000
     Total force =     0.000116     Total SCF correction =     0.000001
     Total force =     0.000146     Total SCF correction =     0.000000
     Total force =     0.000180     Total SCF correction =     0.000001
     Total force =     0.000195     Total SCF correction =     0.000000
     Total force =     0.000193     Total SCF correction =     0.000001
     Total force =     0.000194     Total SCF correction =     0.000001
     Total force =     0.000208     Total SCF correction =     0.000000
     Total force =     0.000271     Total SCF correction =     0.000001
     Total force =     0.000336     Total SCF correction =     0.000000
     Total force =     0.000350     Total SCF correction =     0.000001
     Total force =     0.000355     Total SCF correction =     0.000001
     Total force =     0.000356     Total SCF correction =     0.000001
     Total force =     0.000351     Total SCF correction =     0.000000
     Total force =     0.000364     Total SCF correction =     0.000000
     Total force =     0.000437     Total SCF correction =     0.000000
     Total force =     0.000509     Total SCF correction =     0.000000
     Total force =     0.000542     Total SCF correction =     0.000002
     Total force =     0.000520     Total SCF correction =     0.000001
----------------------------------------------------------------------------
-------------


I also previously tried without ecfixed, qcutz, q2sigma options but the
force did not converge as well.
Any suggestions would be greatly appreciated.
Thank you.

Sincerely,

JISEOK KIM, Ph.D.
Postdoctoral Research Associate
Department of Materials Science and Engineering
University of Texas at Dallas
800 W. Campbell Rd. RL10
Richardson, TX 75080



-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20120904/a0016c76/attachment.html>


More information about the users mailing list