Dear PWSCF users,
<br>
<br>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?
<br>
<br>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.
<br>
<br>Thank you very much,
<br>
<br>Merlin Meheut
<br>LMTG, University Paul Sabatier, Toulouse III
<br>
<br>
<br>My input file is:
<br>
<br>&control
<br>      calculation = 'relax',
<br>    restart_mode = 'from_scratch' ,
<br>           prefix = 'SIDIS',
<br>          disk_io = 'default' ,
<br>   pseudo_dir     = './',
<br>   outdir         = '<i class="moz-txt-slash"><span class="moz-txt-tag">/</span>workdir/lmtg_mm<span class="moz-txt-tag">/</span></i>',
<br>   tprnfor        = .true.,
<br>   tstress        = .true.,
<br>          nstep   =  300,
<br>             dt   =  30,
<br>/&end
<br>&system
<br>   ibrav=0, celldm(1)=9.0,
<br>   nat =33 ,ntyp = 3, ecutwfc =80.0
<br>/&end
<br>&electrons
<br>  electron_maxstep = 30,
<br>         conv_thr = 1.d-7,
<br>      mixing_mode = 'plain',
<br>      startingwfc = 'atomic',
<br>      mixing_beta = 0.5,
<br>/&end
<br>&ions
<br>/&end
<br>&cell
<br>cell_dynamics='damp-w',
<br>wmass=0.01,
<br>press_conv_thr=0.5
<br>/&end
<br>ATOMIC_SPECIES
<br> Si   27.9769   Si.pbe2
<br> O    15.9949   O.pbe
<br> H     1.0079   H.pbe2
<br>ATOMIC_POSITIONS (angstrom)
<br>Si      -0.055773130   0.063041141  -0.019456368
<br>O       -0.928244325   1.220211626   0.742585740
<br>H       -1.918437433   2.227264952  -0.121748599     ----> H atom 
considered
<br>O        0.837697042   0.834495021  -1.203452886
<br>H        1.419897286   0.214362348  -1.779582316
<br>O       -0.976442964  -1.062017620  -0.815312763
<br>H       -1.443585392  -1.793543819  -0.202321297
<br>O        0.875026714  -0.699563815   1.082530768
<br>H        1.374593316  -0.129758653   1.783289887
<br>O       -2.523030520   2.842152567  -0.649494713
<br>H        1.374593316  -0.129758653   1.783289887
<br>O       -2.523030520   2.842152567  -0.649494713     -----> O atom 
considered
<br>H       -2.000610052   2.862502362  -1.508268947
<br>H       -3.359011200   2.320632097  -0.803429871
<br>O        2.374744823  -0.730427393  -2.657582377
<br>H        1.812420975  -1.562743814  -2.724298789
<br>H        3.173301447  -0.956959091  -2.100529884
<br>O       -2.070437190  -2.843623143   0.640995839
<br>H       -1.458242605  -2.949201319   1.425483033
<br>H       -2.082587534  -3.726595208   0.175359266
<br>O        2.029869676   0.759161627   2.917796227
<br>H        1.376285560   1.496846308   3.072591712
<br>H        2.123890300   0.271489220   3.776502975
<br>O       -0.600561577   2.848486026  -2.538060604
<br>H       -0.028982929   2.172971372  -2.080997503
<br>H       -0.483819412   2.639939930  -3.523840473
<br>O        0.401910995  -2.565855954  -2.787840675
<br>H       -0.163488513  -2.095198648  -2.115540255
<br>H        0.335609978  -3.545849462  -2.578258595
<br>O       -0.034585701  -2.892730661   2.496352697
<br>H        0.438090880  -2.165237892   1.997625690
<br>H       -0.094987807  -2.591742169   3.444279646
<br>O       -0.095253507   2.562096056   2.989386942
<br>H       -0.548456386   2.057212509   2.255240882
<br>H       -0.098954519   3.521303327   2.696580855
<br>K_POINTS {automatic}
<br>2 2 2 1 1 1
<br>CELL_PARAMETERS
<br>  1.156195179  -0.063234679  -0.030584446
<br> -0.111384909   1.702090338   0.009939799
<br> -0.055084797   0.010055538   1.690706987
<br>CONSTRAINTS
<br>1 0.05
<br>distance   3    10 

<br>
<br clear="all"><br>-<br>