[QE-users] Unit of macroscopic average in average.x calculations

[Giovanni Cantele]

Hi,

from the header of PP/src/average.f90
  !      Note that if Q is a charge density whose integral is Z_v:
  !         Z_v = \int p(z) dV = \sum_k p(k) \Omega/N_3
  !      where \Omega is the size of the unit cell (or supercell)

So, if I remember, the units should be au^-3, while the horizontal axis is
au.

Just to cross check, take the planar average of a given system (e.g. your
eterostructure) and integrate the 1D function as is.
Supposing that you chose idir = 3 and that a3 is orthogonal to a1,a2, you
should get the number of electrons divider by the surface of
the unit cell defined by a1 and a2.

Let me know.
Giovanni

-- 

Prof. Giovanni Cantele
Dipartimento di Fisica "Ettore Pancini"
Universita' degli Studi di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at unina
Phone: +39 081 676910

Web page: https://sites.google.com/view/giovanni-cantele/home


Il giorno mer 8 ott 2025 alle ore 11:26 jkmodi22 <jkmodi22 at iitk.ac.in> ha
scritto:

> Dear QE users,
>
> I was trying to calculate the planar-averaged charge density difference
> for heterostructure CdCl2-SiH. I was trying to reproduce Figure 5b) of the
> reference paper "Versatility of the SiH−CdCl2Heterostructure:
> Piezoelectricity, Photocatalysis, and Transistor Applications".
>
> I calculated the planar averaged charge density for the hetero-structure,
> then for monolayer SiH, then for CdCl2.
>
> Then delta_rho(z) was calculated = planar averaged charge density for the
> hetero-structure - planar averaged charge density for SiH - planar averaged
> charge density for CdCl2.
>
> My question is, *what is the unit of the third column of average.out
> files?* *is it e/Bohr?* I know the first column is in Bohr.
>
> pp.x page says this :
>
> All output quantities are in ATOMIC (RYDBERG) UNITS unless
> otherwise explicitly specified.
> All charge densities integrate to the NUMBER of electrons
> not to the total charge.
> All potentials have the dimension of an energy (e*V, not V).
>
>
> Therefore, I guessed the third column to be e/Bohr by equation no. 5 of
> the reference paper, which calculates delta_Q(z) as an integral of
> delta_rho(z)
>
>
>
> Thanking you.
>
> Sincerely,
>
> Jainandan Modi
> Ph.D. scholar
> EE Dept.
> IIT Kanpur
> India
>
>
>
>
>
>
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