[Pw_forum] CONSTRAINTS card

[merlin meheut]

Dear PWSCF users,

I am trying the CONSTRAINTS card, and I am not sure that I am understanding
it, because it does not do what I would like: I would like the distance
between an O atom and an H atom not to move more than 0.05 angstrom form its
initial position, during a relaxation. In particular, I am not sure of the
unit of the {constr_tol } variable: is that in ao, a.u., angstrom?

When I am relaxing the structure, the O-H distance changes from 1.001 to 1.6
angstrom, which is obviously not what I thought I asked.

Thank you very much,

Merlin Meheut
LMTG, University Paul Sabatier, Toulouse III


My input file is:

&control
      calculation = 'relax',
    restart_mode = 'from_scratch' ,
           prefix = 'SIDIS',
          disk_io = 'default' ,
   pseudo_dir     = './',
   outdir         = '*/workdir/lmtg_mm/*',
   tprnfor        = .true.,
   tstress        = .true.,
          nstep   =  300,
             dt   =  30,
/&end
&system
   ibrav=0, celldm(1)=9.0,
   nat =33 ,ntyp = 3, ecutwfc =80.0
/&end
&electrons
  electron_maxstep = 30,
         conv_thr = 1.d-7,
      mixing_mode = 'plain',
      startingwfc = 'atomic',
      mixing_beta = 0.5,
/&end
&ions
/&end
&cell
cell_dynamics='damp-w',
wmass=0.01,
press_conv_thr=0.5
/&end
ATOMIC_SPECIES
 Si   27.9769   Si.pbe2
 O    15.9949   O.pbe
 H     1.0079   H.pbe2
ATOMIC_POSITIONS (angstrom)
Si      -0.055773130   0.063041141  -0.019456368
O       -0.928244325   1.220211626   0.742585740
H       -1.918437433   2.227264952  -0.121748599     ----> H atom considered

O        0.837697042   0.834495021  -1.203452886
H        1.419897286   0.214362348  -1.779582316
O       -0.976442964  -1.062017620  -0.815312763
H       -1.443585392  -1.793543819  -0.202321297
O        0.875026714  -0.699563815   1.082530768
H        1.374593316  -0.129758653   1.783289887
O       -2.523030520   2.842152567  -0.649494713
H        1.374593316  -0.129758653   1.783289887
O       -2.523030520   2.842152567  -0.649494713     -----> O atom
considered
H       -2.000610052   2.862502362  -1.508268947
H       -3.359011200   2.320632097  -0.803429871
O        2.374744823  -0.730427393  -2.657582377
H        1.812420975  -1.562743814  -2.724298789
H        3.173301447  -0.956959091  -2.100529884
O       -2.070437190  -2.843623143   0.640995839
H       -1.458242605  -2.949201319   1.425483033
H       -2.082587534  -3.726595208   0.175359266
O        2.029869676   0.759161627   2.917796227
H        1.376285560   1.496846308   3.072591712
H        2.123890300   0.271489220   3.776502975
O       -0.600561577   2.848486026  -2.538060604
H       -0.028982929   2.172971372  -2.080997503
H       -0.483819412   2.639939930  -3.523840473
O        0.401910995  -2.565855954  -2.787840675
H       -0.163488513  -2.095198648  -2.115540255
H        0.335609978  -3.545849462  -2.578258595
O       -0.034585701  -2.892730661   2.496352697
H        0.438090880  -2.165237892   1.997625690
H       -0.094987807  -2.591742169   3.444279646
O       -0.095253507   2.562096056   2.989386942
H       -0.548456386   2.057212509   2.255240882
H       -0.098954519   3.521303327   2.696580855
K_POINTS {automatic}
2 2 2 1 1 1
CELL_PARAMETERS
  1.156195179  -0.063234679  -0.030584446
 -0.111384909   1.702090338   0.009939799
 -0.055084797   0.010055538   1.690706987
CONSTRAINTS
1 0.05
distance   3    10


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