PSOLVER WAVELET for 2D

[mpol]

Dear CP2k users and developers,

I'm interested in using "PSOLVER WAVELET" for slab modeling. The system is 
non-periodic in Y-direction (as needed) and the slab is located between 
6.0≤y and y≤14.0 Å. I'm trying to investigate the convergence of the total 
energy with respect to b cell vector. Impressively, the total energy seems 
to be well-converged with b=20.0 Å, but with b=28.0 or 44.0 Å the E_total 
significantly differs. The dispersion energy is numerically equal in all 
cases examined.

b length, Å                   E_total, a.u.

     20.0               -3380.78353207374357

     24.0               -3380.78353271772994

     *28.0           -3380.83933281508052*

     32.0               -3380.78353203624874

     36.0               -3380.78353278766372

     40.0               -3380.78353202202788

     *44.0           -3380.77895354453995*

     48.0               -3380.78353267361763

*Why **does** this happen?*

Input parameters are:

&FORCE_EVAL
  METHOD QS
  &DFT
    BASIS_SET_FILE_NAME [path to the file]
    POTENTIAL_FILE_NAME [path to the file]
    &MGRID
      NGRIDS 5
      CUTOFF 600
      REL_CUTOFF 60
    &END MGRID
    &PRINT
      &MO
 ADD_LAST SYMBOLIC
 EIGENVALUES
 NDIGITS 8
 OCCUPATION_NUMBERS
 &EACH
  GEO_OPT 1
  QS_SCF 0
 &END EACH
      &END MO
    &END PRINT
     UKS .TRUE.
     MULTIP 3
    &QS
      EPS_DEFAULT 1.0E-14
      METHOD GPW
    &END QS
    &POISSON
 PERIODIC XZ
 PSOLVER WAVELET
 &WAVELET
    SCF_TYPE 100
 &END
    &END POISSON
    &SCF
      EPS_EIGVAL 1.0E-10
      SCF_GUESS RESTART
      EPS_SCF 1.0E-06
      MAX_SCF 1
      &DIAGONALIZATION
        ALGORITHM STANDARD
        MAX_ITER 5
      &END DIAGONALIZATION
      &SMEAR
        FIXED_MAGNETIC_MOMENT 2.0
 METHOD FERMI_DIRAC
 ELECTRONIC_TEMPERATURE 298.0
      &END SMEAR
      ADDED_MOS 32
    &END SCF
    &XC
      &XC_FUNCTIONAL TPSS
      &END XC_FUNCTIONAL
      &vdW_POTENTIAL
         DISPERSION_FUNCTIONAL PAIR_POTENTIAL
         &PAIR_POTENTIAL
            TYPE DFTD3
            PARAMETER_FILE_NAME [path to the file]
            REFERENCE_FUNCTIONAL TPSS
            CALCULATE_C9_TERM .TRUE.
            &PRINT_DFTD SILENT
      COMMON_ITERATION_LEVELS 100
            &END
         &END PAIR_POTENTIAL
      &END vdW_POTENTIAL
    &END XC
  &END DFT
  &SUBSYS
    &CELL
    PERIODIC XZ
      ABC 22.10400 [y] 25.52400
       &END CELL
    &TOPOLOGY
 &CENTER_COORDINATES .FALSE.
 &END
    &END TOPOLOGY
    &COORD
[atomic coordinates]
    &END COORD
[KIND sections with the parameters needed]
  &END SUBSYS

&END FORCE_EVAL
&GLOBAL
  RUN_TYPE ENERGY
  PRINT_LEVEL MEDIUM
  &TIMINGS
     THRESHOLD 0.000001
  &END
  &DBCSR
    MM_DRIVER BLAS
  &END
  PREFERRED_FFT_LIBRARY FFTSG
&END GLOBAL

With best regards,
MP
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