[CP2K-user] [CP2K:16682] Problems of external potential and meta-MD wall

[Bai Li]

Dear CP2K Users,

I want to do a MD simulation about a reaction of two molecules, where the 
two molecules contain a O and a C respectively. I needed to prevent these 
two atoms (O and C in two molecules respectively) moving more than 3 
angstrom from each other. So I find two methods that might work, but I 
don't know which one is applicative or I need to connect both of the 
following methods together.

5 and 9 is the atom O and C. X0, Y0, Z0 in external potential section is 
the coordinates of atom 5.
1. Using External potential section. 
   &EXTERNAL_POTENTIAL
     ATOMS_LIST   9
     FUNCTION     A*(Z-Z0)^8
     PARAMETERS   A Z0
     VALUES       0.001  0.347
     UNITS        eV angstrom
   &END
   &EXTERNAL_POTENTIAL
     ATOMS_LIST   9
     FUNCTION     A*(X-X0)^8
     PARAMETERS   A X0
     VALUES       0.001  1.091
     UNITS        eV angstrom
   &END
   &EXTERNAL_POTENTIAL
     ATOMS_LIST   9
     FUNCTION     A*(Y-Y0)^8
     PARAMETERS   A Y0
     VALUES       0.001  0.062
     UNITS        eV angstrom

For the second methods, I just want to apply the Wall without doing 
Meta-MD, so I close the DO_HILLS 
2. Using Meta-MD Wall section.
    &METADYN
      DO_HILLS .FALSE.
      NT_HILLS 10000
      &METAVAR
        SCALE 0.2
        COLVAR 1
        &WALL
          POSITION [angstrom] 3.0
          TYPE QUARTIC
          &QUARTIC
            DIRECTION WALL_PLUS
            K  [kcalmol] 40.0
          &END QUARTIC
        &END WALL
      &END METAVAR
...........
     &COLVAR
       &COORDINATION
         ATOMS_FROM  5
         ATOMS_TO   9
         R_0 [angstrom]  3.0
         NN  8
         ND  14
       &END COORDINATION
     &END COLVAR
   &END SUBSYS

If someone have time to give me some advices, i would appreciate it.
Best regards

Bai

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