[CP2K-user] [CP2K:21063] Question about total and molecular dipoles

[Fangyong Yan]

Dear Hana,

Wannier function is only for periodic systems. (see for example, our paper:
Infrared Spectroscopy of Li+ Solvation in EmimBF4 and in Propylene
Carbonate: Ab Initio Molecular Dynamics and Experiment, JPCB, 2022)
The wannier center is treated as the expectation value of the position of
individual electrons. That is why we can obtain molecules, or cation
with +1 charge, and anion with -1 charge. Because
all the charges (electrons, nuclei), are integer.
Wannier function is one way to partition the electron density, there are
other methods to partition the charge density.

For a molecule, the dipole moment is invariant to your chosen origin. For a
cation or anion, dipole is dependent on your origin, but the change of
dipole is not, and IR intensity is related to the change of dipole.

Good luck!!

Fangyong


On Sat, Jan 18, 2025 at 12:40 PM Hana <holiaei2 at illinois.edu> wrote:

> Hello,
>
> I am trying to calculate the dipole moment of my non-periodic system. The
> system has more than one molecule, and I am interested in calculating both
> molecular and total dipole moment. Currently, I use two sections (section1:
> FORCE_EVAL/DFT/LOCALIZE, section 2: FORCE_EVAL/DFT/PRINT/MOMENTS) in my
> input, as elaborated at the end of this message. Section 2 outputs a total
> dipole moment of 18.9465 Debye. From section 1 and using the Wannier
> centers, I get a total dipole moment of 18.9876 Debye. Here is my first
> question: Is this discrepancy normal? According to CP2K documentation, the
> first value (from section 2) is based on "simple operator". However, I am
> not sure what that is, and whether it justifies the discrepancy?
>
> Also, I have another question. In section 1, I have the TOTAL_DIPOLE and
> MOLECULAR_DIPOLES subsections as well. The dipole values that I get from
> these two are completely (orders of magnitude) different from the values
> mentioned in the previous paragraph (~19 Debye), although I set all the
> reference points to zero. Moreover, for the molecular dipole, the output
> file shows zero for most of the atoms, and non-zero values for the rest of
> them. Therefore, I cannot find the "molecule" concept there. Here is my
> second question: Am I missing anything when using these two subsections
> (TOTAL_DIPOLE and MOLECULAR_DIPOLES)?
>
> Thanks in advance for your help, and sorry for the long message!
>
> *section 1:*
>     &LOCALIZE
>       MAX_ITER 1000
>       METHOD JACOBI
>       EPS_LOCALIZATION 1.0E-6
>       &PRINT
>         &WANNIER_CENTERS
>            IONS+CENTERS .TRUE.
>         &END
>         &TOTAL_DIPOLE
>            PERIODIC F
>            REFERENCE ZERO
>            FILENAME total
>         &END
>         &MOLECULAR_DIPOLES
>            PERIODIC F
>            REFERENCE ZERO
>            FILENAME molecular
>         &END
>       &END
>     &END
>
> *section 2:*
>     &PRINT
>       &MOMENTS
>             PERIODIC F
>             REFERENCE ZERO
>             FILENAME dipole
>       &END
>     &END
>
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