[Pw_forum] Saw tooth potential details

[mohamed sabri majdoub]

Dear users,

I was reading the documentation for the saw tooth like potential in pwscf.
However, I still did not understood it in full. Can anybody gives me more
details about how the potential is implemented.
I need to apply an electric field to a supercell of graphene and BN layers
with both ends in vacuum. eamp = 0.002.


Amplitude of the electric field (in a.u. = 51.44 10^10 V/m )
The sawlike potential increases with slope "eamp" in the
region from (emaxpos+eopreg-1) to (emaxpos), then decreases
to 0 until (emaxpos+eopreg), in units of the crystal
vector "edir". Important: the change of slope of this
potential must be located in the empty region, or else
unphysical forces will result. Used only if tefield is .TRUE.

The following keywords that need to be used are still not clear. In
particular the position of the slope change.Does it need to be in vacuum?
emaxpos=0.5 (Position of the maximum of the sawlike potential along
crystal axis
"edir"); eopreg=0.5 (Zone in the unit cell where the sawlike potential
decreases.)?
How the sawlike potential is modeled.
Thank you in advance for your help and comment.

Here is the system I want to apply electric field to it:

&control
             title = 'GphBN'
       calculation = 'relax'
            outdir = '/pwscf/pwscftemp/relaxGphBN'
            prefix = 'GphBN'
        pseudo_dir = /pwscf/input/Gph-BN/pseudopot-C-B-N'
         verbosity = 'high'
          tprnfor  = .t.
      restart_mode = 'from_scratch'

 /
 &system
             ibrav = 0,
         celldm(1) = 1.8897261
               nat = 72,
              ntyp = 3,
           ecutwfc = 25.0
           ecutrho = 250.0
       occupations = 'smearing'
          smearing = 'gaussian'
           degauss = 0.003675

 /
 &electrons
    mixing_beta = 0.05
    diagonalization = 'david'

 /
 &ions
  trust_radius_ini = 0.10

 /
 &cell

ATOMIC_SPECIES
 B    10.81100   B.pz-vbc.UPF
 C    12.01070   C.pz-vbc.UPF
 N    14.00674   N.pz-vbc.UPF
ATOMIC_POSITIONS angstrom
 B         0.710000        8.607000       11.306000
 B         0.710000       11.066000       11.306000
 B         2.840000        7.377000       11.306000
 B         0.710000        6.148000       11.306000
 B         6.390000        6.148000        8.000000
 B         6.390000        8.607000        8.000000
 B         6.390000       11.066000        8.000000
 B         2.840000        9.836000       11.306000
 B         7.100000        7.377000       11.306000
 B         7.100000        9.836000       11.306000
 B         7.100000       12.295000       11.306000
 B         4.970000       11.066000       11.306000
 B         2.840000       12.295000       11.306000
 B         4.970000        6.148000       11.306000
 B         4.970000        8.607000       11.306000
 B         4.260000        7.377000        8.000000
 B         2.130000       11.066000        8.000000
 B         2.130000        8.607000        8.000000
 B         2.130000        6.148000        8.000000
 B         4.260000        9.836000        8.000000
 B         0.000000        7.377000        8.000000
 B         0.000000        9.836000        8.000000
 B         4.260000       12.295000        8.000000
 B         0.000000       12.295000        8.000000
 C         2.130000        6.148000       14.612000
 C         2.130000        8.607000       14.612000
 C         2.130000       11.066000       14.612000
 C         0.000000       12.295000       14.612000
 C         0.000000        9.836000       14.612000
 C         0.000000        7.377000       14.612000
 C         0.710000       11.066000       14.612000
 C         0.710000        8.607000       14.612000
 C         0.710000        6.148000       14.612000
 C         6.390000        8.607000       14.612000
 C         6.390000        6.148000       14.612000
 C         4.970000       11.066000       14.612000
 C         6.390000       11.066000       14.612000
 C         7.100000       12.295000       14.612000
 C         7.100000        9.836000       14.612000
 C         7.100000        7.377000       14.612000
 C         4.970000        8.607000       14.612000
 C         2.840000       12.295000       14.612000
 C         2.840000        9.836000       14.612000
 C         2.840000        7.377000       14.612000
 C         4.260000        7.377000       14.612000
 C         4.970000        6.148000       14.612000
 C         4.260000       12.295000       14.612000
 C         4.260000        9.836000       14.612000
 N         0.000000       12.295000       11.306000
 N         0.000000        9.836000       11.306000
 N         0.000000        7.377000       11.306000
 N         2.840000        7.377000        8.000000
 N         2.840000        9.836000        8.000000
 N         2.840000       12.295000        8.000000
 N         4.970000       11.066000        8.000000
 N         4.970000        8.607000        8.000000
 N         4.970000        6.148000        8.000000
 N         7.100000       12.295000        8.000000
 N         7.100000        9.836000        8.000000
 N         7.100000        7.377000        8.000000
 N         0.710000        6.148000        8.000000
 N         0.710000        8.607000        8.000000
 N         0.710000       11.066000        8.000000
 N         6.390000       11.066000       11.306000
 N         6.390000        8.607000       11.306000
 N         6.390000        6.148000       11.306000
 N         2.130000       11.066000       11.306000
 N         2.130000        8.607000       11.306000
 N         2.130000        6.148000       11.306000
 N         4.260000       12.295000       11.306000
 N         4.260000        9.836000       11.306000
 N         4.260000        7.377000       11.306000
K_POINTS automatic
10 10 1 1 1 0
CELL_PARAMETERS
8.51980 0.00000 0.00000
0.00000 7.37600 0.00000
0.00000 0.00000 22.6120
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