drift of center of mass

[Wei Lai]

Dear cp2k users and developers,

 

I am testing a NVE simulation with velocity scaling for crystalline CaO 
(300 K) and having questions regarding the drift of center of mass.

 

In a regular NVE simulation, I am expecting that (1) the simulation box is 
fixed and positions of atoms can be in fractional/scaled or Cartesian 
units, (2) if atoms moved out of the simulation box, they can be folded 
back to the box or left unchanged, (3) the mass-averaged position centers 
oscillate around x, y, z direction.  I am showing the center of mass 
positions from VASP, which are consistent with the expectation.


<https://lh3.googleusercontent.com/-tRDdhXVYalE/WGxP2ScXNBI/AAAAAAAAhnk/8bGLtoxRwxINxHoXywkIJFBPOkR4IipMwCLcB/s1600/cp2k-vs-VASP.TIF>



 

If I do the same for cp2k (input file enclosed), I am clearly seeing drift 
of center of mass.  If I analyze the dynamics of the trajectory (now 
shown), it appears that both Ca and O atoms are diffusing instead of 
vibrating, as obtained from VASP trajectory.

 

I am wondering if you have seen similar behaviors or if I have the wrong 
settings in the input file.

 

Thanks, Wei
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