[Pw_forum] on variable cell optimization

[Eduardo Ariel Menendez P]

Hello,
I am trying to perorm a variable cell optimization, but I do nont know how
to relax the stress.
At the beginnig I have this stress report
     entering subroutine stress ...

          total   stress  (ryd/bohr**3)                  (kbar)     P=
-65.91
  -0.00046851  -0.00000003   0.00000033        -68.92     -0.01      0.05
  -0.00000003  -0.00046821  -0.00000018         -0.01    -68.88     -0.03
   0.00000033  -0.00000018  -0.00040740          0.05     -0.03    -59.93

And after 12 steps I have this:

     entering subroutine stress ...

          total   stress  (ryd/bohr**3)                  (kbar)     P=
-65.91
  -0.00046853  -0.00000004   0.00000033        -68.92     -0.01      0.05
  -0.00000004  -0.00046825  -0.00000019         -0.01    -68.88     -0.03
   0.00000033  -0.00000019  -0.00040737          0.05     -0.03    -59.93

There is no stress oscillation in the intermediate steps, the forces are
below the force threshold forc_conv_thr  REAL ( default = 1.0D-3 )
and the energy histort seems converged as defined by the deault threshold
etot_conv_thr  REAL ( default = 1.0D-4 )
!    total energy              =  -762.00561350 ryd
!    total energy              =  -762.00561283 ryd
!    total energy              =  -762.00560983 ryd
!    total energy              =  -762.00560492 ryd
!    total energy              =  -762.00559677 ryd
!    total energy              =  -762.00558778 ryd
!    total energy              =  -762.00557901 ryd
!    total energy              =  -762.00555677 ryd
!    total energy              =  -762.00555691 ryd
!    total energy              =  -762.00551207 ryd
!    total energy              =  -762.00553888 ryd
!    total energy              =  -762.00544708 ryd

Please, tell me why the stress is not released, and why the simulation
does not stop.


This is the input file

 &control
    calculation='vc-relax'
    restart_mode='from_scratch',
    tstress = .true.
    tprnfor = .true.
    prefix='tisic',
    pseudo_dir = '/home/gonzalo/eariel/Compilaciones/Espresso/pseudo',
    outdir='./'
 /
 &system
    ibrav=  0, celldm(1) =5.7778399,
    nat=  12, ntyp= 3,
    ecutwfc =60.0
    ecutrho = 320.0 ,
    occupations = 'smearing' ,
    degauss = 0.02 ,
    smearing = 'fermi-dirac' ,
 /
 &electrons
    diagonalization='david'
    mixing_mode = 'plain'
    conv_thr =  1.0d-8
    mixing_beta = 0.7
 /
 &ions
    upscale=10
    trust_radius_max = 0.1
    trust_radius_ini = 0.1
 /
 &CELL
 press=0.d0,
 cell_dynamics='damp-w'
 /
ATOMIC_SPECIES
   Ti   47.867  Ti.vdb.UPF
   Si  28.0855  Si-ca-ggjr.UPF
   C   12.010   C.pz-rrkjus.UPF

CELL_PARAMETERS
  1.000000  0.000000  0.000000
 -0.500000  0.866025  0.000000
  0.000000  0.000000  5.764022

ATOMIC_POSITIONS crystal
Ti       0.000000000   0.000000000   0.000000000
Ti       0.000000716  -0.000449249   0.499925429
Ti       0.666423342   0.333262850   0.133989450
Ti       0.333333000   0.666667000   0.633906018
Ti       0.333295794   0.666847382   0.866005352
Ti       0.666623159   0.332895739   0.365913496
Si      -0.000234387  -0.000347156   0.249920409
Si       0.000000000   0.000000000   0.750000000
C        0.333172599   0.666627154   0.072080546
C        0.666669370   0.333119893   0.571915905
C        0.666633759   0.333400448   0.927992237
C        0.333314765   0.666070328   0.427808834

K_POINTS automatic
 10 10 2   0 0 0

Thanks

Eduardo A. Menendez Proupin
Department of Physics
Faculty of Science
University of Chile
Las Palmeras 3425
Ñuñoa, Santiago
Chile
Phone: 56+2+678 74 11
http://fisica.ciencias.uchile.cl/~emenendez/