[Pw_forum] Fwd: Fourier component of charge density with and without the electric field

[Mudit Dixit]

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. I
can to obtain the charge density difference as a matrix on FFT grid to
plot. However, in the paper(doi:10.1038/nature11340) the authors have
obtained the charge density difference as a number (They say "By comparing
the Fourier component of charge density with and without the electric field
we calculate the charge density difference (i.e. induced charge). The
induced charge density ρ(G111,E=3.4x108)-ρ(G111,E=0) equals 1.07x10-4
e/Å3"). I am unable to understand it.

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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