[CP2K-user] Was periodic_efield designed to work with DFTB?

[W. Lai]

Dear cp2k users/developers,

I am wondering if the function of applying electric field through 
"periodic_efield" was designed to also work with DFTB.  I simply took the 
H2O-efiled.inp from tests/QS/regtest-p-efield and modified it to use DFTB 
(parameters from data/DFTB/scc).  I was using version 7.1.

I am comparing the Mulliken charges from cp2k-DFT, cp2k-DFTB, and also from 
DFTB+.  Apparently, results from cp2k-DFTB under the field are a little odd.

Thanks, Wei

efield:                                                              
 -0.01                  0                         0.01
Mulliken charge (cp2k-DFT):                 -0.389706          -0.426154    
       -0.461808
Mulliken charge (cp2k-DFTB):               0.060747          -0.547117      
    -1.089736
Mulliken charge (DFTB+):                       -0.525336         -0.547117  
        -0.568806 

&FORCE_EVAL
  METHOD Quickstep
  &DFT
    &PRINT
      &MOMENTS
        PERIODIC T
      &END
    &END
    SURFACE_DIPOLE_CORRECTION
    SURF_DIP_DIR Z
    &PERIODIC_EFIELD
       POLARISATION 0 0 1
       INTENSITY -0.01
    &END    
    &QS
      METHOD DFTB
      &DFTB
        SELF_CONSISTENT    T
        DO_EWALD           T
        DISPERSION         F
        &PARAMETER
            SK_FILE H H     ./H-H.skf
            SK_FILE H O     ./H-O.skf
            SK_FILE O H     ./O-H.skf
            SK_FILE O O     ./O-O.skf
        &END PARAMETER
      &END DFTB
    &END QS
    &SCF
      EPS_SCF 1.0E-6
      SCF_GUESS MOPAC
      MAX_SCF 100
      &OT
        PRECONDITIONER FULL_ALL
      &END
    &END SCF
    &POISSON
      PERIODIC XYZ
      &EWALD
        EWALD_TYPE SPME
        ALPHA  .35
        GMAX   41
      &END EWALD        
    &END POISSON
  &END DFT
  &SUBSYS
    &TOPOLOGY
    &CENTER_COORDINATES
    &END
    &END
    &CELL
      ABC 16.0 16.0 16.0
    &END CELL
    &COORD
    O   0.000000    0.000000   -0.065587 H2O
    H   0.000000   -0.757136    0.520545 H2O
    H   0.000000    0.757136    0.520545 H2O
    &END COORD
  &END SUBSYS
&END FORCE_EVAL
&GLOBAL
  PROJECT H2O-field
  PRINT_LEVEL MEDIUM
  RUN_TYPE ENERGY
&END GLOBAL



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