[QE-users] Doping

[Giovanni Cantele]

It is possible to simulate a doped system. However, the only way to do it is using a supercell approach.

Indeed, doping is usually meant as a “random” distribution of non-interacting (or almost non-interacting)
impurities. As such, you should choose a sufficiently large supercell (for example, try 2x2x2 or 3x3x3 for
a three-dimensional cubic lattice), to prevent the impurity defects in neighbour supercells from interacting.

Consider that if in the bulk unit cell you sample the Brillouin zone with a n x n x n k-point grid and study
the impurity with an m x m x m supercell, the latter requires, to obtain the same accuracy with
respect to the sampling, a n/m x n/m x n/m k-point grid (for example, if you use a 6x6x6 k-point grid in the
1x1x1 bulk unit cell, and study the impurity within a 2x2x2 supercell, for the latter you sample the BZ with
a 3x3x3 k-point grid).

This being said, the larger the supercell, the larger the computational resources (also in terms of RAM)
you need.

If you use, as you say, a “unit cell structure” (I think you mean the same unit cell as the bulk crystal),
you are simulating a possibly interacting distribution of impurities, with concentrations usually much larger
that the experimental ones and with defect levels that possibly exhibit dispersion (“defect bands”).

Giovanni

PS people usually do sign their posts in the forum, together with their affiliation.

> On 8 Jul 2020, at 20:32, Neelam Swarnkar <neelamswarnkar35 at gmail.com> wrote:
> 
> Dear expert and all
> 
> Doping of an atom is possible in a unit cell structure, because supercell taking a lot RAM for calculation.
> 
> If it is possible , than please let me know.
> 
> Thanks in advance
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-- 

Giovanni Cantele, PhD

CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy

e-mail: giovanni.cantele at spin.cnr.it
            gcantele at gmail.com
Phone: +39 081 676910
Skype contact: giocan74
Web page: https://sites.google.com/view/giovanni-cantele

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