[CP2K-user] How to set constant speed of atoms with constrain?

[yghua... at gmail.com]

Hi, everyone: 

I am trying to simulate the transportation of atom through a membrane, in 
which the *scalar *speed  (mode of velocity) should be set as constant. 
But I really do not know how to set this constant speed condition in CP2K. 
If you have any idea, please give me a hand. Many thanks!

If this is difficult, I should also try the second best as set the Velocity 
in a direction as constant. 
I am wondering whether I can constrain the the distance of the atom to a 
fixed point to be increased at specific value in each time step?

In the following example, I *set a constrain *on the distance in the x 
direction from No.409 atom to the fixed point at (4,  7, 7) to *increase 
0.01 Angstrom with each MD step*.  

such as : 

#-----Colvar-------
   &COLVAR
       *&Distance*
       &Point
        Atoms 409
        Type Geo_center
       &End Point
       &Point
        Type Fix_point
        xyz [angstrom] 4  7 7
       &End Point
       Points 1, 2
       Axis x
       &END Distance

   &END COLVAR
  &END SUBSYS


 &MOTION
#===================
   &Constraint
    &Collective
     Colvar 1
     Intermolecular
     Target 0
     Target_limit 25
     Target_Growth  0.01
    &End Collective
    #Constraint_init .True.
    &Constraint_info
     Filename = constraint.inf
    &END Constraint_info
   &END Constraint
#===================
    &MD
     ENSEMBLE NVE
     STEPS 500
     TIMESTEP 0.1
  &END MD

But it seems do not run as I thinking. 

Thanks for any reply, suggestion and comment. 
Best regards, 

Y. Huang                                                                    
                                                                            
                                                                      
224,19        98%

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