[Pw_forum] Is the constrain card avaible?

[Lu Yunhao]

I set the constrains card in input file to constrain the distance between
two atoms in relaxation, but the it does not work at all. I am not sure
what's wrong. Is there anyone can help me? Thanks!
 The input file is included as follows:

&CONTROL
                       title = 'CO_O2' ,
                 calculation = 'relax' ,
                prefix='CO_O2-con',
                restart_mode = 'from_scratch' ,
                      outdir =
'/home/phylyh/00-Au-catalysis/CO_O2-constrain/tmp' ,
                  pseudo_dir = '/home/phylyh/pseudo_dir' ,
                  disk_io = 'none',
                  etot_conv_thr = 1.0D-5,
                  forc_conv_thr = 1.0D-4, 
/
 &SYSTEM
                       ibrav = 0,
                         nat = 76,
                        ntyp = 3,
                     ecutwfc = 30 ,
                     ecutrho = 300 ,
                     nosym = .false. ,
                     nspin = 2,
                     starting_magnetization(2) = 0.7 ,
                     starting_magnetization(3) = 0.7 ,
                     occupations='smearing',
                     smearing='gauss',
                     degauss=0.01,
 /
 &ELECTRONS
  conv_thr    = 1.D-6,
  mixing_mode = 'local-TF',
  mixing_beta = 0.8D0,
  mixing_ndim = 8,
  diagonalization = 'david' ,
electron_maxstep = 500
/
&IONS
ion_dynamics = 'bfgs',
upscale = 18.0, 
bfgs_ndim = 1,
trust_radius_max = 0.8D0,
trust_radius_min = 1.D-3,
trust_radius_ini = 0.5D0,
w_1 = 0.01D0,
w_2 = 0.5D0,
pot_extrapolation = "second_order",
/
CELL_PARAMETERS cubic
24.18234040895346130     -13.96168074474439     0.000000000000000
0.000000000000000       27.9233614894888667     0.000000000000000
0.000000000000000       0.000000000000000       37.7945232712218137894 
ATOMIC_SPECIES
    C    1.00000   C.pbe-rrkjus.UPF
    O    1.00000   O.pbe-rrkjus.UPF
   Au    1.00000   Au.pbe-nd-van.UPF
ATOMIC_POSITIONS crystal 
  C   0.0011800000211225   0.0029599999543280   0.3677699863910680
  C   0.1123699992895130   0.0584199987351895   0.3688299953937530
  C   0.1679899990558620   0.0030400000978262   0.3671199977397920
....
....
  C   0.9457899928092950   0.8917999863624572   0.3670699894428250
  C   0.5544400215148930   0.6150699853897090   0.5497099757194520
  O   0.4347901741294347   0.4590097156291522   0.5539600253105161
  O   0.5039499998092650   0.4248099923133851   0.5561699867248540
  O   0.5783299803733830   0.6644200086593630   0.5974799990653990
 Au   0.4996399879455560   0.5032899975776670   0.4675300121307370
K_POINTS  gamma
CONSTRAINTS
1   1.D-8 
distance    72   73