[Pw_forum] Saw tooth potential details

TuanAnh Pham ptanhphys at gmail.com
Thu Dec 17 00:59:01 CET 2009


Dear Mohamed,

This is one example:
- In &control: You should add
    tefield = .true.
    dipfield = .true.
The second is dipole correction
- In &system, you should add
    edir = 3            ! This is the direction of applied field
    eamp = 0.002  ! Amplitude of e-field-should be small
    emaxpos = 0.9
    eopreg = 0.2
In this way, the potential increase from (emaxpos+eopreg-1)=0.1 to (emaxpos)
= 0.9
then decrease to 0 until (emaxpos+eopreg)=1.1 (in the units of the crystal
vector edir).
You can draw this to see why it is called sawtooth potential.
It is better to have your system in the middle of the super-cell, and the
vacuum
region should be large enough so that you can *make sure* that your system
lies between
(emaxpos+eopreg-1) and (emaxpos+eopreg).
The change of slope *must* be in the vacuum region.
You can find some more information here:  R. Resta and K. Kunc, Phys. Rev. B
34, 7146 (1986)

Good luck,

On Wed, Dec 16, 2009 at 2:24 PM, mohamed sabri majdoub <majdoub at gmail.com>wrote:

> 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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> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>
>


-- 
Tuan Anh Pham
Department of Chemistry
University of California, Davis
Phone: 530-752-0957
Homepage: http://angstrom.ucdavis.edu/
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