&FORCE_EVAL
  METHOD FIST
  &MM
    &FORCEFIELD
      parm_file_name ../sample_pot/water.pot
      parmtype CHM
      &CHARGE
        ATOM OT
        CHARGE -0.8476
      &END CHARGE
      &CHARGE
        ATOM HT
        CHARGE 0.4238
      &END CHARGE
      &SPLINE
        EMAX_SPLINE 1.0
      &END
    &END FORCEFIELD
    &POISSON
      &EWALD
        EWALD_TYPE pme
        ALPHA .44
        NS_MAX 25
      &END EWALD
    &END POISSON
  &END MM
  &SUBSYS
    &CELL
      ABC 24.955 24.955 24.955
    &END CELL
    &COLVAR
      &DISTANCE_FUNCTION
        &POINT
          TYPE GEO_CENTER
          ATOMS 4
        &END
        &POINT
          TYPE GEO_CENTER
          ATOMS 6
        &END
        &POINT
          TYPE GEO_CENTER
          ATOMS 6
        &END
        &POINT
          TYPE GEO_CENTER
          ATOMS 1
        &END
        ATOMS 1 2 3 4
        # distance 1 = ( 4 - 6 )
        # distance 2 = ( 6 - 1 )
        COEFFICIENT -1.0000
      &END DISTANCE_FUNCTION
    &END COLVAR
    &TOPOLOGY
      COORD_FILE_NAME ../sample_xyz/water_2.xyz
      COORDINATE xyz
      &GENERATE
        REORDER
        CREATE_MOLECULES
      &END
    &END TOPOLOGY
  &END SUBSYS
&END FORCE_EVAL
&GLOBAL
  PROJECT water_3_ddist_g
  RUN_TYPE MD
&END GLOBAL
&MOTION
  &CONSTRAINT
    &COLLECTIVE
      TARGET -3.78
      INTERMOLECULAR
      COLVAR 1
    &END COLLECTIVE
  &END CONSTRAINT
  &MD
    ENSEMBLE NVE
    STEPS 10
    TIMESTEP 2.5
    TEMPERATURE 298
  &END MD
&END MOTION
