[CP2K-user] [CP2K:15636] Re: Dipole Moment. Help wanted.

Alexander Kazakov alexande... at gmail.com
Tue Jun 29 09:59:48 UTC 2021

Dear Mr. Hutter,

thank you for your reply!

I am reading now 2 papers:
* Nicola A. Spaldin DOI: 10.1016/j.jssc.2012.05.010 -- more about the 
problem of calculation dipole moment (polarization)
* Konstantin N. Kudin, Roberto Car, and Raffaele Resta DOI: 

Can you, please, suggest more relevant literature?

@Reference point
Are you talking about this: 

I see there 4 points which could be a good options, however, all of them 
has good default values:

* REFERENCE                   Default value: ZERO
* REFERENCE_2               Default value: ZERO
* REFERENCE_POINT      Default values: 0.00000000E+000 0.00000000E+000 
* REFERENCE_POINT_2  Default values: 0.00000000E+000 0.00000000E+000 

I am not sure that some others values can bring some benefits for the 
simple cubic system with 64 molecules (sparely distributed).

With best regards,
Alexander Kazakov

понедельник, 28 июня 2021 г. в 10:32:08 UTC+2, jgh: 

> Hi
> dipole moments in periodic systems are only defined modulo 2Pi/L
> (for simple cubic systems). The value is calculated through a
> complex Logarithm that can lead to results on different branches
> with offsets. Have a look at the literature for more complete
> discussions and more general formulas. 
> The choice of reference point can lead to a reduced number of
> "jumps" and easier post-processing. 
> regards
> Juerg Hutter
> --------------------------------------------------------------
> Juerg Hutter Phone : ++41 44 635 4491 <+41%2044%20635%2044%2091>
> Institut für Chemie C FAX : ++41 44 635 6838 <+41%2044%20635%2068%2038>
> Universität Zürich E-mail: h... at chem.uzh.ch
> Winterthurerstrasse 190
> CH-8057 Zürich, Switzerland
> ---------------------------------------------------------------
> -----c... at googlegroups.com wrote: -----
> To: "cp2k" <c... at googlegroups.com>
> From: "Alexander Kazakov" 
> Sent by: c... at googlegroups.com
> Date: 06/25/2021 03:58PM
> Subject: [CP2K:15636] Re: Dipole Moment. Help wanted.
> 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:
> 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)
> 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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> [attachment "W64.xyz" removed by Jürg Hutter/at/UZH]
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