[CP2K:2724] constraint/target

[rupa]

Hi all,
I was trying to understand how the constraint dynamics works in CP2K
for a test case, where  water dimer dissociates into H3O+ and OH-. The
constraint was the O---H bond between both the water molecules, which
is expected to decrease from 1.8 to 1.0 Å.
However, the constraint didn't change during simulation.
However, the reverse reaction scheme i.e. H3O+ + OH- -> (H2O)2, where
O-H bond elongates from 1.0 to 1.8 Å, works fine.
It seems the target growth can only be positive!!!
Please correct if I am wrong.

Thanks
Rupa

input reference for constraint section:
&COLVAR
      &DISTANCE
       ATOMS 1 6
      &END DISTANCE
    &END COLVAR
&END SUBSYS
******
&CONSTRAINT
    &COLLECTIVE
      COLVAR 1
      INTERMOLECULAR T
      TARGET [angstrom] 1.8
      TARGET_GROWTH [angstrom*fs^-1]  0.001
      TARGET_LIMIT [angstrom] 1.0
    &END COLLECTIVE
    &LAGRANGE_MULTIPLIERS ON
     COMMON_ITERATION_LEVELS 3
    &END LAGRANGE_MULTIPLIERS
&END CONSTRAINT


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