[Pw_forum] Applying a perpendicular Electric Field

[Thomas Brumme]

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 fieldin 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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