[CP2K-user] [CP2K:17126] Energy differences when a molecule with a dipole moment is moved through a PBC

[alex van der waals]

Hi,

I've been seeing a strange effect from a calculation. I have a single CO 
molecule, that I am displacing through the Z axis of a 5x5x10, 2x2x10 and a 
1x1x10 PBC (with periodicity on for all axes, angles=90 degrees for all), 
and doing single point energy calculations for each. I expect that because 
its periodic, there should be no difference in energy where in the PBC I 
put the CO molecule. Strangely however, there is an energy difference; as I 
scan the Z axis, the energy reported fluctuates up and down periodically. I 
am using the PBE functional  and a cutoff=300 fwiw.

I have attached figures and input files for the calcultions below.

Is this a known phenomenon?
Best,
Alex

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