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