[CP2K-user] Dipole Moment. Help wanted.

Alexander Kazakov alexande... at gmail.com
Fri Jun 25 13:58:39 UTC 2021

Yeap. Topology is here.

Best regards,
Alexander Kazakov

пятница, 25 июня 2021 г. в 15:55:24 UTC+2, Alexander Kazakov: 

> Dear CP2K community,
> I am simulating 64 molecules of water using DFT in NVT ensemble using PBC. 
> I interested in dipole moment values as a trajectory with MD step. 
> Here is what I have so far:
> [image: DM_xyz_total.png]
> You can see 4 curves: 3 of them are components (x,y,z) and the last one is 
> the length of the vector.  All of them are functions of the MD step.
> Let's focus on curves that correspond to x and z components. You can see 
> that there is a kind of "jump"  at certain ranges. These "jump" actually 
> resemble a crossing kind of boundary condition. You can see how well it is 
> fit the blue curve on the top to the bottom (the same is applied for the 
> purple curve).
> Personally, I think it is indeed a kind of boundary condition, however, I 
> have no idea what 30 means.
> Then I found these certain steps where it happens:
> 26
>     X=  -19.18787840 Y=    5.85693184 Z=   29.55510907     Total=    
> 35.72090144 
> 27
>     X=  -19.18076162 Y=    5.52351367 Z=  -29.53176935     Total=    
> 35.64458192
> So the z component apparently changed the sign. So I thought that 
> something horrible happened in the system. I plotted position atom change 
> as a function of atom ID:
> (if the picture has very poor quality, please find enclosed pdf version)
> [image: 26-27_diff.png]
> Alright, there is an interesting plot here. We see the different amplitude 
> of change through the atom IDs. So first 2/3 of the curve correspond to 
> hydrogen atoms displacement, whereas the last part corresponds to oxygen 
> atoms.
> *So back to questions.* Could you tell me, why some components of the 
> dipole moment "jump" changing the sigh? Is it possible to force dipole 
> moment to stay on one side of the "boundary"? There are no doubts that 
> hydrogen atoms should move "actively" than oxygen atoms, but I don't 
> understand what has changed dramatically in the system. Lastly, if you can 
> give me a hint for number 30 in the boundary (see figure), I would be 
> thankful!
> As because I check CP2K 6.1, 7.1, 8.1, and 8.2 and I got the same 
> behaviour with jumps I assume that I did something wrong or misunderstand 
> something.
> Please find enclosed FORCE_EVAL section of my script.
> Additionally I am sending topology of the system.
> If additionaly information is required, please let me know.
> Best regards,
> Alexander Kazakov
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