[CP2K-user] [CP2K:17127] Re: Energy differences when a molecule with a dipole moment is moved through a PBC

[alex van der waals]

Sorry, I should clarify the files attached. In Z-align, the CO molecule is 
aligned with the Z axis; Zperp is perpendicular to the Z axis. In the 
*closepack files, the PBC is 1x1x10, whereas in the others it is 5x5x10. 
The results are in the plot folder; where the figure 
Z-align-closepack.txt.png plots the energy difference as a function of Z 
displacement; a variation of 0.12 Hartrees is seen. In all the other 
experiments, the variation is much smaller, 0.001 Hartrees. 

Best,
Alex


On Friday, 10 June 2022 at 15:09:18 UTC-4 alex van der waals wrote:

> 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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