[Pw_forum] Applying a perpendicular Electric Field

[Bahadır salmankurt]

Dear Dr. Thomas Brumme,

Thank you again. I never forget this :)

2015-11-20 16:51 GMT+02:00 Thomas Brumme <thomas.brumme at mpsd.mpg.de>:

> Dear Bahadır,
>
> the input file seems to be OK. Nevertheless, you always have to test in
> the end
> that no charge is spilling into the vacuum because the sawtooth function is
> creating an artificial potential minimum. Do this by plotting to total
> potential
> (pp.x, plot_num=1) for example as 3D data file and using average.x to
> average
> over the in-plane directions. If charge is spilling the potential is not
> linear in the
> vacuum region or shows other weird behavior. In this case you have to
> reduce
> the vacuum region in order to reduce the depth of the artificial minimum.
> This
> on the other hand can lead (for too large electric fields) to a vacuum
> region
> which is too small, i.e., leading to interactions between the repeated
> slabs.
>
> The wrong gap you get can be due to anything - your initial input file was
> just
> wrong. The sawtooth within the slab itself is an unphysical situation.
>
> Regards
>
> Thomas
>
>
> P.S.: You're using an ultrasoft pseudopotential. In such cases ecutrho
> needs to
> be larger than just 4 times ecutwfc. More like 10 times... Which is also
> stated in
> the documentation...
>
>
> On 11/20/2015 03:27 PM, Bahadır salmankurt wrote:
>
> Dear Dr. Thomas Brumme,
>
> Thank you for clear explanation.
>
> And also I have changed my input file. now, Is everything ok?
>
> ****
> &control
>     calculation='scf'
>     restart_mode='from_scratch',
>     prefix='As',
>     tstress = .true.
>     tprnfor = .true.
>     pseudo_dir ='/home/hakan/tubitak/espresso-5.2.0/pseudo/',
>     outdir='/home/hakan/tubitak/As/efield/out/',
> !           etot_conv_thr = 1.0E-4,
> !           forc_conv_thr = 1.0D-3,
>      wf_collect=.true.,
> !     verbosity='high',
> tefield=.true.
> *dipfield=.true.*
>  /
> &system
> nbnd=10,
>     ibrav=0,celldm(1)=1.8897,
>     nat= 2, ntyp=1,
>     ecutwfc =30.0,
>     ecutrho=120,
> *  emaxpos=0.95,*
>   eopreg=0.10,
>   edir = 3,
>  eamp = 0.0105,
>    /
> ...
>
> ****
>
> By the way, the difference is that  , when E field was applied under 5.00
> V/nm ( eamp = 0.0097 au) E field in prb paper which I shared , the band
> gap became about 0.80 eV. But I find this band gap under 10.5 V/nm
> (eamp=0.0205 au) E field ( I have used new input data).
>
> what does the reason such a difference happen?
>
> Thank you again..
>
>
> --
> Dr. rer. nat. Thomas Brumme
> Max Planck Institute for the Structure and Dynamics of Matter
> Luruper Chaussee 149
> 22761 Hamburg
>
> Tel:  +49 (0)40 8998 6557
>
> email: Thomas.Brumme at mpsd.mpg.de
>
>
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>



-- 

Bahadır SALMANKURT
PhD student
Sakarya University, TURKEY
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