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

Fri Feb 21 15:33:12 CET 2014

```Dear Mudit,

I couldn’t find a ‘charge density difference plot’ in supplementary information but I assume they just calculated the charge density for those two structures that you mentioned, and subtracted from each other. The result can be plotted as a distribution of charge in 3D (2D) or you can add up the values to get a number for different regions [but again I think total number is still zero].

Please have a closer look in the pp.x input file [plot_num, nfile, weight …] to see how you can do this. Also there are many similar issues from the past if you search the forum.

Best,

From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On Behalf Of Mudit Dixit
Sent: 21 February 2014 13:28
To: PWSCF Forum
Subject: Re: [Pw_forum] Charge density with and without the electric field

​​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<mailto: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<tel:%2B353%2021%20234%206972>
Website: http://www.tyndall.ie<http://www.tyndall.ie/>

.

From: pw_forum-bounces at pwscf.org<mailto:pw_forum-bounces at pwscf.org> [mailto: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<mailto: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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