[DFTB-Plus-User] Graphene under electric field

[Dongkyu Lee]

Dear DFTB+ users,

I am trying to check Pz to Pz hamiltonian changes of AA stacking graphene
under E-field.
But there is some weirdness in my results. Although the lattice vector of
the c axis is large enough and the boundary is in a vacuum state, The value
of the hamiltonian changes significantly depending on the location of
graphene. Even though the DFT(Quantum ESPRESSO) results show very little
change with respect to the electric field.
I wonder if I'm misapplying the electric field

Here are my input files  ===================
"dftb_in.hsd"
Geometry = GenFormat {
<<< geo.gen
}

Hamiltonian = DFTB {
SCC = Yes
MaxAngularMomentum = {
    C = "p"
}
Filling = Fermi {
    Temperature [Kelvin] = 1
}
SlaterKosterFiles = Type2FileNames {
    Prefix = "../SLAKO/matsci/"
    Separator = "-"
    Suffix = ".skf"
}
ElectricField = {
    External = {
    Strength = 0.002
    Direction = 0.0 0.0 1.0
    }
}
KPointsAndWeights = SuperCellFolding {
    19 0 0
    0 19 0
    0 0 1
    0.0 0.0 0.0
}
Dispersion = DftD4{
    s6 = 1.0
    s8 = 3.3157614
    s9 = 1
    a1 = 0.4826330
    a2 = 5.3811976
}
}

"geo.gen" - 1st try
 4  S
 C
    1  1    0.1423934080E+01    0.0000000000E+00    23.6150510539E+00
    2  1    0.2847868160E+01    0.0000000000E+00    23.6150322381E+00
    3  1    0.1423934080E+01    0.0000000000E+00    2.6734958389E+01
    4  1    0.2847868160E+01    0.0000000000E+00    2.6734958319E+01
    0.0000000000E+00    0.0000000000E+00    0.0000000000E+00
    0.2135959681E+01   -0.1233409085E+01    0.0000000000E+00
    0.2135959681E+01    0.1233409085E+01    0.0000000000E+00
   -0.0000000000E+00    0.0000000000E+00    0.4988144214E+02

"geo.gen" - 2nd try
 4  S
 C
    1  1    0.1423934080E+01    0.2437979894E-11    10.1150510539E+00
    2  1   -0.1423934081E+01   -0.2421080327E-11    10.1150322381E+00
    3  1    0.1423934079E+01   -0.2056833083E-10    1.3234958389E+01
    4  1   -0.1423934079E+01    0.2055287066E-10    1.3234958319E+01
    0.0000000000E+00    0.0000000000E+00    0.0000000000E+00
    0.2135959681E+01   -0.1233409085E+01   -0.3405712312E-14
    0.2135959681E+01    0.1233409085E+01    0.2463894179E-14
   -0.2232943453E-20    0.1028856612E-27    0.4988144214E+02

Here my results =================
For 1st try, Pz-Pz hamiltonian between 3rd-4th atom
E = 0  : -1.224835621105427E-01 [Hartree]
E = 0.002 : -1.074191917297013E-01 [Hartree]

For 2nd try, Pz-Pz hamiltonian between 3rd-4th atom
E = 0  : -1.224835621105427E-01 [Hartree]
E = 0.002 : -1.150260485442335E-01 [Hartree]
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