# [CP2K-user] Dipole Moment. Help wanted.

Alexander Kazakov alexande... at gmail.com
Fri Jun 25 13:55:23 UTC 2021

```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:

MD STEP
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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&FORCE_EVAL
METHOD QS
STRESS_TENSOR ANALYTICAL
! TEST https://groups.google.com/g/cp2k/c/eM_ShSf4wkw/m/03iRUCOGAgAJ
&PROPERTIES
&LINRES
&LOCALIZE
&PRINT
&TOTAL_DIPOLE
PERIODIC .FALSE.
&END
&MOLECULAR_DIPOLES
PERIODIC .FALSE.
&END
&END
&END
&END
&END
! TEST
&DFT
BASIS_SET_FILE_NAME \${BASIS_FILENAME}
POTENTIAL_FILE_NAME \${POTENTIAL_FILENAME}
@IF ( \${RESTART} == TRUE )
WFN_RESTART_FILE_NAME \${WAVEFILE}
@ENDIF
! multigrids calculations
&MGRID
CUTOFF \${MGRID_CUTOFF_VALUE}
NGRIDS \${GRIDS}
&END MGRID
&PRINT
&MOMENTS
FILENAME moments
&END
&END
&QS
METHOD GPW
&END QS
@INCLUDE './static/scf.inc'
&XC
&XC_FUNCTIONAL \${XC_FUNCTIONAL_NAME} #PBE
&END XC_FUNCTIONAL
@IF ( \${HF} == TRUE )
&HF ! Sets up the Hartree-Fock parameters if requested
FRACTION                  1.0       ! Default [1.0] The fraction of Hartree-Fock to add to the total energy. 1.0 implies standard Hartree-Fock if used with XC_FUNCTIONAL NONE.
! NOTE: In a mixed potential calculation this should be set to 1.0, otherwise all parts are multiplied with this factor.
&SCREENING
EPS_SCHWARZ           1.0E-8    ! Default [1e-10] Screens the near field part of the electronic repulsion integrals using the Schwarz inequality for the given threshold.
SCREEN_ON_INITIAL_P   TRUE      ! Default [F]     Screen on an initial density matrix. For the first MD step this matrix must be provided by a Restart File. |?
&END SCREENING
&INTERACTION_POTENTIAL
POTENTIAL_TYPE        TRUNCATED ! Default [COULOMB] Which interaction potential should be used (Coulomb, longrange or shortrange).
! COULOMB:       Coulomb potential: 1/r
! GAUSSIAN:      Damped Gaussian potential: exp(-omega^2*r^2)
! IDENTITY:      Overlap
! LONGRANGE:     Longrange potential: erf(omega*r)/r
! MIX_CL:        Mix coulomb and longrange potential: 1/r + erf(omega*r)/r
! MIX_CL_TRUNC:  Truncated Mix coulomb and longrange potential, assumes/requires that the erf has fully decayed at R_c
! MIX_LG:        Mix Gaussian and longrange potential: erf(omega*r)/r + exp(-omega^2*r^2)
! SHORTRANGE:    Shortrange potential: erfc(omega*r)/r
! TRUNCATED:     Truncated coulomb potential: if (r < R_c) 1/r else 0

CUTOFF_RADIUS         \${HF_CUTOFF_RADIUS}  ! Default [angstrom] Determines cutoff radius for the truncated 1/r potential. Only valid when doing truncated calculation
T_C_G_DATA            ./static/t_c_g.dat   ! Location of the file t_c_g.dat that contains the data for the evaluation of the truncated gamma function
&END
&MEMORY
MAX_MEMORY \${HF_MEMORY_MiB}    ! Default [512] Defines the maximum amount of memory [MiB] to be consumed by the full HFX module.
! All temporary buffers and helper arrays are subtracted from this number. What remains will be used for storage of integrals.
! NOTE: This number is assumed to represent the memory available to one MPI process.
! When running a threaded version, cp2k automatically takes care of distributing the memory among all the threads within a process.
&END
&END HF
@ENDIF
@IF ( \${RIMP2} == TRUE )
&WF_CORRELATION   ! Sets up the wavefunction-based correlation methods as MP2, RI-MP2, RI-SOS-MP2, RI-RPA and GW (inside RI-RPA)
&RI_MP2
&END RI_MP2
&INTEGRALS    ! Parameters controlling how to compute integrals that are needed in MP2, RI-MP2, RI-RPA, RI-SOS-MP2 and GW (inside RI-RPA).
&WFC_GPW  ! Parameters for the GPW approach in Wavefunction-based Correlation methods
CUTOFF      \${MP2_CUTOFF_VALUE}   ! Default [300]  The cutoff of the finest grid level in the MP2 gpw integration.
REL_CUTOFF  50                    ! Default [50]   Determines the grid at which a Gaussian is mapped.
EPS_FILTER  1.0E-12               ! Default [1e-9] Determines a threshold for the DBCSR based multiply (usually 10 times smaller than EPS_GRID).Normally, this EPS_FILTER determines accuracy and timing of cubic-scaling RPA calculation.
EPS_GRID    1.0E-8                ! Default [1e-8] Determines a threshold for the GPW based integration
&END
&END INTEGRALS
MEMORY      \${MP2_MEMORY_MiB} ! Default [1024]  Maximum allowed total memory [MiB] usage during MP2 methods
GROUP_SIZE  1                 ! Default [1]     number of MPI ranks per node accelerates computations
&END
@ENDIF
&END XC
&END DFT
@INCLUDE './static/subsys.inc'
&END FORCE_EVAL
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