[Pw_forum] sawlike potential in supercell calculation

[lan haiping]

you can draw a saw potential by hand, which will help you understand.
 for you question , ［0，1］ of coz define the whole supercell under your
examination.



On Thu, Jun 5, 2008 at 5:23 AM, <Mohamed.Majdoub at mail.uh.edu> wrote:

> Dear users,
>
> I really find difficulties in understanding and ambiguities on how the saw
> like potential is implemented in pwscf. I need to apply an external electric
> filed to a slab structure in supercell (including vacuum region) in the z
> direction (edir =3) of amplitude eamp.According to the manual, besides
> setting tefiled and dipfield (dipole correction for slab) to be true, we
> need to specify the following variables in &system:
> ------------------------------------------------------------------------
> edir           INTEGER
>
>                The direction of the electric field or dipole correction is
>                parallel to the bg(:,edir) reciprocal lattice vector, so the
>                potential is constant in planes defined by FFT grid points;
>                edir = 1, 2 or 3. Used only if tefield is .TRUE.
>
> emaxpos        REAL ( default = 0.5D0 )
>
>                Position of the maximum of the sawlike potential along
> crystal
>                axis "edir", within the  unit cell (see below), 0 < emaxpos
> < 1
>                Used only if tefield is .TRUE.
>
> eopreg         REAL( default = 0.1D0 )
>
>                Zone in the unit cell where the sawlike potential decreases.
>                ( see below, 0 < eopreg < 1 ). Used only if tefield is
> .TRUE.
>
> eamp           REAL ( default = 0.001 a.u. ) 0.000001 a.u
>
>                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". Used only if tefield is .TRUE.
> ---------------------------------------------------------------------
> Since it is external electric field it shoud be only applied to the vacuum
> region in the supercell as it was pointed out before (
> http://www.democritos.it/pipermail/pw_forum/2004-July/001169.html).
> However, it is not clear if the 0< x<1 interval is the vacuum interval or
> the full length of the supercell (structure + vacuum). How the decrease in
> the sawlike potential is defined? Is it in the slab or the vaccum?
> Can any one familiar with this kind of calculation explain how it is
> implemented?
>
> Thank you in advance!
>
> Mohamed Sabri Majdoub
> PhD mechanical engineering
> University of Houston
> Houston, Tx, USA
>
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>


-- 
Hai-Ping Lan
Department of Electronics ,
Peking University , Bejing, 100871
lanhaiping at gmail.com, hplan at pku.edu.cn
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