# [Pw_forum] Charge density with and without the electric field

Mudit Dixit dixitmuditk at gmail.com
Fri Feb 21 14:27:47 CET 2014

```Dear Hadi Arefi,
​​Thanks for the quick response.
In the second point I meant that in the paper"
http://www.nature.com/nature/journal/v488/n7413/full/nature11340.html"
authors have calculated induced charge as
​
ρ(G111,E=X)-ρ(G111,E=0).They have also shown the charge
density difference plot in supporting information. I am unable
to understand how they have obtained the induced charge as a number.

​Thank you so much for your help.
Regards,
Mudit Dixit​

On 21 February 2014 18:27, Hadi Arefi <hadi.arefi at tyndall.ie> wrote:

>  Dear Mudit,
>
>
>
>
>
> >My questions are following:
>
> >1. How apply electric filed in 111 direction.
>
>
>
> You simply can redefine your lattice in the way that (111) direction lies
> along one of the x, y or z direction, then apply the field along that
> direction.
>
>
>
> >2. How
> ​​
> ρ(G111,E=X)-ρ(G111,E=0) give a number not an array on FFT grid.
>
>
>
> Not quite sure what you mean but obviously the difference going to be an
> array which you can plot using xcrysden. My understanding is that you did
> not add external charge by applying electric field and the difference in
> charge density will rises from charge reorganisation due to external field
> (if there is any) unless you are interested in the local differences. Then
> you have the 3D mesh and need to find your points and subtract the values
> of equivalent points with and without applying field and then summation.
>
>
>
> HTH,
>
>
>
>
>
>
> PhD student
>
> Electronic theory&modeling group
>
> *Tyndall National Institute*
>
> University College Cork
>
> Lee Maltings
>
>
> Cork, Ireland
>
> Tel: +353 21 234 6972
>
> Email: *hadi.arefi at tyndall.ie <hadi.arefi at tyndall.ie>*
>
> Website: http://www.tyndall.ie
>
> [image: cid:image001.jpg at 01CBEADB.24D1AE90] <http://www.tyndall.ie/>
>
>
>
> .
>
>
>
>
>
> *From:* pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] *On
> Behalf Of *Mudit Dixit
> *Sent:* 20 February 2014 09:11
> *To:* pw_forum at pwscf.org
> *Subject:* [Pw_forum] Charge density with and without the electric field
>
>
>
> Dear PW users,
>
> I am trying to calculate charge density difference (i.e. induced charge)
> in presence of Electric Field(G111 direction) and absence of electric
> filed.
>
>
>
> My questions are following:
>
> 1. How apply electric filed in 111 direction.
>
> 2. How ρ(G111,E=X)-ρ(G111,E=0) give a number not an array on FFT grid.
>
>
>
> Thanks a lot for your help.
>
>
>
>
>
> Regards,
>
> Mudit
>
>
>
>
>
>
>
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