[Pw_forum] How to do vc-relax in CP code?

[程迎春]

Dear all,
      In the namelist of control, it seems that CP code can do a lot of
calculations(scf, nscf,relax,vc-relax,vc-cp,...).   I have tested the
example18, which shows how to use cp.x to perform molecular dynamics
simulation of SiO2.  The first step is to get the ground state of the
electronic system.  I think there should be a previous step to get the
equilibrium structure of SiO2.  However I find there isn't any examples to
do vc-relax using CP code.  If I want to CP code to do vc-relax calculation,
how to set corresponding parameters?  In PW code, the vc-relax calculation
is done in temperature=0 K condition which ignore the kinetic energy of
ions. But in CP code, the vc-relax calculation  complains that the
temperature can not be 0 K. So I set the temperatures of ions and cell are
'not_controlled'.  In the 'not_controlled' calculation, the cell of the
system expands with the increasing steps. It is strange.  How to do vc-relax
in CP code?  The following is the input file and some information from
output file.
input
 &control
    calculation='vc-relax',
    restart_mode='from_scratch',
    nstep=100,
    iprint=1,
    isave=1,
    dt=8.0,
    ndr=91,
    ndw=92,
    pseudo_dir='./',
    outdir='./',
 /
 &system
    ibrav=8,
    celldm(1)=9.28990,
    celldm(2)=1.73206,
     celldm(3)=1.09955,
    nat=18,
     ntyp=2,
     nbnd=48,
     nelec=96,
     nspin=1,
    ecutwfc=20.0,
    ecutrho=150.0,
    nr1b=16,
    nr2b=16,
    nr3b=16,
    qcutz=150.,
    q2sigma=2.0,
    ecfixed=16.0,
 /
 &electrons
    electron_dynamics='verlet',
    ortho_max=100,
    emass=700.,
    emass_cutoff=3.,
 /
 &ions
    ion_dynamics='verlet',
    ion_radius(1)=1.0,
    ion_radius(2)=1.0,
 /
 &cell
    cell_dynamics='pr',
    press=0.D0
 /
ATOMIC_SPECIES
   O  16.00 O.pz-rrkjus.UPF
  Si  28.00 Si.vbc.UPF
ATOMIC_POSITIONS
 O  3.18829368  14.83237039   1.22882961
 O  7.83231469   6.78704039   1.22882961
 O  2.07443467   5.99537992   4.73758250
 O  6.72031366  14.04231898   4.73758250
 O  3.96307134  11.26989826   7.87860582
 O  8.60802134   3.22295920   7.87860582
 O  3.96307134   4.81915267   9.14625133
 O  8.60802134  12.86448267   9.14625133
 O  3.18736469   1.25668055   5.58029607
 O  7.83324368   9.30201055   5.58029607
 O  2.07536366  10.09206195   2.07358613
 O  6.71938467   2.04673195   2.07358613
Si  0.28891589   8.04533000   3.40456284
Si  4.93386589   0.00000000   3.40456284
Si  2.13389003  12.27717358  -0.04188031
Si  6.77884003   4.23184358  -0.04188031
Si  2.13389003   3.81348642   6.85202747
Si  6.77884003  11.85881642   6.85202747

some information form output file
step 1
   CELL_PARAMETERS
    9.28990000    0.00000000    0.00000000
    0.00000000   16.09066419    0.00000000
    0.00000000    0.00000000   10.21470954

   Total stress (GPa)
     1582.97951906        -1.16929980       -21.68011687
       -1.17872209      1618.59651136        11.14345397
      -21.82861949        11.00777251      1647.98672617


step 50
   CELL_PARAMETERS
   16.77885645   -0.00946391    0.01423662
   -0.01456595   21.79804238   -0.00448412
    0.01470088   -0.00304592   17.53521234
   Total stress (GPa)
      -11.78865891         0.58606252         1.97796694
        0.58606252        95.04276174        -4.47537576
        1.97796694        -4.47537576         7.30569481

step 100
   CELL_PARAMETERS
   26.25499658   -0.05592615    0.05092035
   -0.07610163   31.84643730    0.00083894
    0.05276954    0.00223134   27.45646153
   Total stress (GPa)
      -21.80901098         0.11600975        -0.06986058
        0.11600975        -1.12040472         0.25103238
       -0.06986058         0.25103238       -19.41116556
-- 
Y. C. Cheng
Department of Physics
Nanjing University
Nanjing 210093
P. R. China
Tel: 86-25-83592907
Email: yccheng.nju at gmail.com
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