Can you combine QMMM with a constraint?

[Steven Turner]

Hi all,

I am currently trying to run a QM/MM simulation using CP2K with Gromacs. Running the simulation alone works fine, but I would like to add a distance restraint or constraint to pull two QM modelled atoms together. Below is the relevant input parameters i have used, but no pulling effect is observed (Note that the numbers have been set very high just for testing purposes). I'm unsure if it is possible to constrain a system when performing a FORCE_EVAL?

Any ideas or assistance from the community would be most appreciated.

    &COLVAR
      &DISTANCE
        ATOMS 33293 3157
      &END DISTANCE
      &PRINT
      &END
    &END COLVAR
  &END SUBSYS
&END FORCE_EVAL
&MOTION
  &CONSTRAINT
    &CONSTRAINT_INFO
      COMMON_ITERATION_LEVELS 3
      FILENAME COLVAR_CONSTR.OUT
      &EACH
        MD 1
      &END
    &END
    &COLLECTIVE
      COLVAR 1
      INTERMOLECULAR T
      TARGET [angstrom] 3.9
      TARGET_GROWTH [angstrom*fs^-1] -50.00
      TARGET_LIMIT [angstrom] 2.0
    &END
  &END
&END

Many thanks,

Steven

[Marcella Iannuzzi]

Dear Steven, 

There should be no problem in applying constraints in a QM/MM simulation,

but if you are using the interface between Gromacs and CP2K,  the dynamics is driven by Gromacs

not by CP2K. 

Regards

Marcella