[CP2K-user] [CP2K:16124] Some questions related to dipole moment in CP2K

[Kaixuan Chen]

Hi All,
I am currently interested in calculating the dipole moment using CP2K.
Based on what I found, there are several ways to output dipole moment in 
CP2K, but all of them differ from each other. Namely three dipoles: 1) 
Total dipole 
(https://manual.cp2k.org/cp2k-8_1-branch/CP2K_INPUT/FORCE_EVAL/DFT/LOCALIZE/PRINT/TOTAL_DIPOLE.html); 
2) Molecular dipole 
(https://manual.cp2k.org/cp2k-8_1-branch/CP2K_INPUT/FORCE_EVAL/DFT/LOCALIZE/PRINT/MOLECULAR_DIPOLES.html); 
3) moments 
(https://manual.cp2k.org/cp2k-8_1-branch/CP2K_INPUT/FORCE_EVAL/DFT/PRINT/MOMENTS.html).
1. What puzzles me most is the difference between total dipole and moments. 
For example, for small molecule such as a single H2O- anion in a 12 
angstrom cubic box. I think the water dipole moment is supposed to be the 
same to the total dipole of the system. But the output of total dipole and 
moment from CP2K is not the same, how can this be explained?
2. What does the molecular dipole mean, or how it is calculated? I assume 
it is calculated by simply nuclear charge times atomic coordinate? Is this 
correct? Since clearly the check sum of molecular dipole doesn't match 
either total dipole or moment.
3. Why can one use the second reference point 
(https://manual.cp2k.org/cp2k-8_1-branch/CP2K_INPUT/FORCE_EVAL/DFT/PRINT/MOMENTS.html#REFERENCE_2)? 
How does the second reference point work?

Any suggestions or comments are welcome. Thanks in advance.

With regards, Kai

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