[CP2K-user] [CP2K:21553] Forces not equivariant upon molecule rotation

[Harry Richardson]

Hi Jürg


Thanks for your reply, I understand there will be limitations to the 
invariance, i.e. not perfectly invariant, but if you glance at the forces 
they do not really seem invariant at all, as in lots of forces are in 
opposite directions etc, do you think I could have set up the input file 
incorrectly or something as I could not see any mistakes? 

Thanks 

Harry 
 



On Tuesday, June 17, 2025 at 8:45:15 AM UTC+1 Jürg Hutter wrote:

> Hi
>
> the periodic Hamiltonian with plane wave basis sets (as partly used in 
> CP2K or in PW codes) is not
> rotationally and translationally (only up to quantas of grid spacings) 
> invariant.
>
> The variation in energy/forces depends on several factors, but exact 
> invariance will only be achieved
> for infinite box size and infinite PW cutoff.
>
> regards
> JH
>
> ________________________________________
> From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of Harry 
> Richardson <harrysgr... at gmail.com>
> Sent: Monday, June 16, 2025 1:07 PM
> To: cp2k
> Subject: [CP2K:21545] Forces not equivariant upon molecule rotation
>
>
> Hi I am running some energy+force calculation of a single benzene molecule 
> using WB97X-D (benzene.inp).
>
> In order to test the equivariance of the force calculations I have rotated 
> the molecule by 180 degrees around the vector [0.5,0.5,0.5] via the file 
> rotation.ipynb.
>
> I then calculate the forces for both (forces_0, forces_180) and use the 
> file equi_checker.ipynb to rotate the forces back to the original space and 
> compare them.
>
> When I do this the forces do not appear equivariant at all, in fact the 
> magnitude of the difference in forces is of the order of the forces 
> themselves i.e. converting force to ev/A:
>
> sum absolute difference 270 deg rotation: 1.651721858651293 eV/A sum 
> absolute difference 180 deg rotation: 1.5320346141088304 eV/A sum absolute 
> difference 90 deg rotation: 0.6562673988482665 eV/A
>
> and this is when the total absolute forces themselves are ~1.55ev/A
>
> Does anyone have any ideas or can see any issues with my input / outputs 
> forces? I have tried tightening convergence and trying different 
> potentials, none seemed to make much difference?
>
> Thank you for any help anyone can provide
>
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