# [Pw_forum] How to get average electrostatic potential?

Giovanni Cantele giovanni.cantele at spin.cnr.it
Wed Oct 16 12:03:17 CEST 2013

```On Oct 16, 2013, at 10:52 AM, Yue-Wen Fang <yuewen.fang at gmail.com> wrote:

> Dear pwscf users,
>
> I have got electrostatic potential, but I want to average the data to make the curve more smoothly like FIG11 in this paper http://prb.aps.org/abstract/PRB/v71/i23/e235317. But I haven't found correct definition of average electrostatic potential from web of science up till now. The problem has also troubled me for several days. I put the data of electric potential alone Z in the attachments. If the data was plotted, it would to be a curve like many waves, but I want to get a average one.
>
> Any suggestion is appreciated.
>  potential-pw.txt
>
>
> --
> ------------------------------------------------------------------------------------------------------------
> Yue-Wen FANG, PhD candidate
> Key Laboratory of Polar Materials and Devices, Ministry of Education
> East China Normal University
>
>
>

You can perform a planar average, which provides, for example in the case of a surface slab,
the potential as a function of the coordinate in the direction normal to the surface itself.
Of course, such a "microscopic average", say V(z), contains oscillations related with the atomistic structure

The "smooth" average you want to build is instead a "macroscopic" average of V(z), which means obtaining
a new function V'(z) where the oscillations are smoothed out when you choose a window for macroscopic average
whose size is comparable with the plane distances.
There are lot of papers describing this average procedure, e.g. PRL 61, 734 (1988); PRB 44, 5572 (1991);
J. Vac. Sci. Technol. B 10, 1744 (1992); PRB 76, 035430 2007 ; ….

See espresso-5.0.2/PP/src/average.f90 for the numerical implementation of such an average procedure
within Quantum-ESPRESSO.

Giovanni

--

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Scienze Fisiche
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele
http://www.nanomat.unina.it

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