Inconsistency in molecular dipole calculation

[Daniele Passerone]

Dear cp2k developers,

We found some inconsistencies while trying to compute the dipole
moments of a set of rather large molecules (about 50 atoms each). We
perform localization then compute the molecular dipoles, all in the
periodic framework of qs.

The problem already starts with a single molecule: when reducing the
unit cell, at a certain point the result contained in the
MOLECULAR_DIPOLES file and the one in TOTAL_DIPOLE dramatically
diverge in one of the components, the former making no sense anymore:

molecule dimensions:  about 11.5 X 10 x 5 [Ang]

cell: 24 x 11.7 x 30    :       Energy          -210.480436477626597
                                        tot. dipole (debye):
0.103426    0.309235   1.012335
                                        mol. dipole (debye):
0.103426    0.309235    1.012335



cell: 23 x 11.7 x 30    :       Energy:          -210.480579307746098
                                        tot.   dipole (debye)
0.1028177    0.308785    1.010828
                                        mol. dipole (debye):
-331.318277   0.308785    1.010828


As you see, as the x dimension of the cell hits twice the size x of
the molecule, then the mol. dipole gets wrong. Curiosly, in the y
direction the cell dimensions are comparable with the molecular size,
but I observe no problem!

I tried different localization algorithms, and I include the input
file (the run takes 4 minutes on 16 cpus, with SZV basis sets).

Thank you for any help,
Daniele


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&FORCE_EVAL
  METHOD Quickstep
  &DFT
    BASIS_SET_FILE_NAME ./BASIS_MOLOPT
    POTENTIAL_FILE_NAME ./GTH_POTENTIALS
    RESTART_FILE_NAME RESTART.wfn
    &QS
      METHOD GPW
      EXTRAPOLATION ASPC
      EXTRAPOLATION_ORDER 3
    &END QS
    &SCF
      MAX_SCF 20
      SCF_GUESS RESTART
      EPS_SCF 1.0E-6
      &OT
        PRECONDITIONER  FULL_SINGLE_INVERSE
        MINIMIZER  DIIS
      &END
      &OUTER_SCF
        MAX_SCF 20
        EPS_SCF 1.0E-6
      &END
    &END SCF
    &XC
      &XC_FUNCTIONAL PBE
      &END XC_FUNCTIONAL
    &END XC
    &LOCALIZE
       EPS_LOCALIZATION 0.00001
       METHOD CRAZY
    &END
    &PRINT
     &LOCALIZATION
      &MOLECULAR_DIPOLES
       ADD_LAST NUMERIC
       &EACH
        QS_SCF 1
       &END
       FILENAME  ./mol_dip
      &END
      &TOTAL_DIPOLE
       FILENAME  ./tot_dip
      &END
     &END
    &END
  &END DFT
  &SUBSYS
    &CELL
    ABC [angstrom]   23 11.7  30
    &END CELL
    &COORD
 N    6.280   9.939  18.195 MOL1
 N   17.807   6.665  20.913 MOL1
 C    8.726   9.186  18.612 MOL1
 C    9.778  10.173  18.679 MOL1
 C    9.473  11.557  18.546 MOL1
 C   10.479  12.485  18.545 MOL1
 C   11.817   12.11  18.846 MOL1
 C   12.855  13.086  18.805 MOL1
 C   14.155  12.723  19.024 MOL1
 C   14.466  11.417  19.502 MOL1
 C   15.820  11.026  19.707 MOL1
 C   16.125   9.767  20.151 MOL1
 C   15.091   8.909  20.626 MOL1
 C   15.401   7.605  21.163 MOL1
 C   14.420   6.826  21.738 MOL1
 C   13.106   7.333  21.914 MOL1
 C   12.146   6.595  22.651 MOL1
 C   10.900   7.128  22.922 MOL1
 C   10.596   8.436  22.491 MOL1
 C   11.507   9.162  21.743 MOL1
 C   12.763   8.619  21.384 MOL1
 C   13.736   9.336  20.584 MOL1
 C   13.416  10.486  19.766 MOL1
 C   12.120  10.753  19.172 MOL1
 C   11.125   9.749  18.861 MOL1
 C   11.423   8.341  18.668 MOL1
 C   12.711    7.85  18.347 MOL1
 C   12.955   6.492  18.228 MOL1
 C   11.919   5.554  18.420 MOL1
 C   10.632   6.002  18.638 MOL1
 C   10.353    7.39  18.718 MOL1
 C    9.008   7.843  18.729 MOL1
 C    7.377   9.598  18.401 MOL1
 C   16.728   7.091  21.044 MOL1
 H    9.639   8.885  22.753 MOL1
 H   12.594  14.109  18.531 MOL1
 H   10.170   6.556  23.495 MOL1
 H   11.257  10.175  21.438 MOL1
 H   17.160   9.429  20.211 MOL1
 H   16.610  11.736  19.456 MOL1
 H   10.267  13.535  18.340 MOL1
 H   13.521   8.552  18.171 MOL1
 H   12.127   4.486  18.348 MOL1
 H   12.422   5.608  23.024 MOL1
 H    9.800     5.3  18.710 MOL1
 H   14.971  13.431  18.879 MOL1
 H    8.199   7.112  18.734 MOL1
 H   14.662    5.83  22.108 MOL1
 H   13.958    6.15  17.975 MOL1
 H    8.437  11.856  18.386 MOL1
    &END
    &TOPOLOGY
      COORD_FILE_FORMAT OFF
    &END
    &KIND C
      BASIS_SET SZV-MOLOPT-GTH
      POTENTIAL GTH-PBE-q4
    &END KIND
    &KIND N
      BASIS_SET SZV-MOLOPT-GTH
      POTENTIAL GTH-PBE-q5
    &END KIND
    &KIND O
      BASIS_SET SZV-MOLOPT-GTH
      POTENTIAL GTH-PBE-q6
    &END KIND
    &KIND H
      BASIS_SET SZV-MOLOPT-GTH
      POTENTIAL GTH-PBE-q1
    &END KIND
  &END SUBSYS
&END FORCE_EVAL
&GLOBAL
  PRINT_LEVEL LOW
  PROJECT LOC
  RUN_TYPE ENERGY
&END GLOBAL