[CP2K-user] Why can not I get the desired band gap when applying external bias to bilayer graphene system

[Tianshu Jiang]

Hi, everyone in cp2k community, 
As the title suggested, I have been calculating band gap of bilayer 
graphene under external bias using cp2k 4.1. 
But the band gap reported in literature can reach 170~190 meV if external 
bias reach 2 V/nm (i.e. 0.2V/angstrom in my setting). 
In my calculation, the band gap can only reach 110~115meV. 
Can anyone give some suggestion ? Here is my input file.

@SET PROJ_NAME bilayerBias_02
@SET BS_NAME biBias_02.bs
@SET IF_USE_EXPOT YES
@SET ELEC_MAGNI 0.2

&GLOBAL
  PROJECT ${PROJ_NAME}
  RUN_TYPE ENERGY
  PRINT_LEVEL MEDIUM
&END GLOBAL

&FORCE_EVAL
  METHOD Quickstep
  &DFT
    BASIS_SET_FILE_NAME BASIS_MOLOPT
POTENTIAL_FILE_NAME POTENTIAL

&MGRID
 NGRIDS 5
 CUTOFF 350
 REL_CUTOFF 60
&END MGRID

&POISSON
 PERIODIC XYZ
&END POISSON
&QS
 EXTRAPOLATION USE_GUESS
&END QS
&SCF
 SCF_GUESS ATOMIC
 EPS_SCF 1.0E-6
 MAX_SCF 300

 ADDED_MOS 2
 &SMEAR ON
   METHOD FERMI_DIRAC
ELECTRONIC_TEMPERATURE [K] 300
 &END SMEAR
 &DIAGONALIZATION
   ALGORITHM STANDARD
EPS_ADAPT 0.01
 &END DIAGONALIZATION
 &MIXING
   METHOD BROYDEN_MIXING
ALPHA 0.2
BETA 1.5
NBROYDEN 8
 &END MIXING
    &END SCF
@IF ( ${IF_USE_EXPOT} == YES )
    &EXTERNAL_POTENTIAL
        FUNCTION (A/B) * Z
VALUES [eV] 0.2  [angstrom] 1.0
    PARAMETERS A B
&END
@ENDIF
&XC
 &XC_FUNCTIONAL PBE
 &END XC_FUNCTIONAL
 &XC_GRID
XC_SMOOTH_RHO NN50
XC_DERIV NN50_SMOOTH
 &END XC_GRID
 &VDW_POTENTIAL
POTENTIAL_TYPE PAIR_POTENTIAL
 &PAIR_POTENTIAL
PARAMETER_FILE_NAME dftd3.dat
TYPE DFTD3
REFERENCE_FUNCTIONAL PBE
R_CUTOFF [angstrom] 16
 &END
 &END VDW_POTENTIAL
&END XC
&KPOINTS
 SCHEME MONKHORST-PACK 11 11 1
      SYMMETRY OFF
 WAVEFUNCTIONS REAL
 FULL_GRID .TRUE.
 PARALLEL_GROUP_SIZE 0
 &BAND_STRUCTURE
ADDED_MOS 4
FILE_NAME ${BS_NAME}
&KPOINT_SET
 UNITS CART_BOHR
          SPECIAL_POINT 0.0 0.0 0.0
          SPECIAL_POINT 1./2. 0.0 0.0
          SPECIAL_POINT 2./3. 1./3. 0.0
          SPECIAL_POINT 0.0 0.0 0.
 NPOINTS 160
&END
 &END BAND_STRUCTURE
&END KPOINTS
  &END DFT
  &SUBSYS
    &CELL
 ABC [angstrom] 2.4612 2.4612 16.75
 ALPHA_BETA_GAMMA 90. 90. 60.
 SYMMETRY HEXAGONAL
 PERIODIC XYZ
 MULTIPLE_UNIT_CELL 1 1 1
&END CELL
&TOPOLOGY
 MULTIPLE_UNIT_CELL 1 1 1
&END TOPOLOGY
&COORD
 SCALED
      C 0.    0.    4./5.
      C 1./3. 1./3. 4./5.
      C 2./3. 2./3. 5./5.
      C 3./3. 3./3. 5./5.
&END
&KIND C
 ELEMENT C
 BASIS_SET TZVP-MOLOPT-GTH
 POTENTIAL GTH-BLYP-q4
&END KIND
  &END SUBSYS

&END FORCE_EVAL



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