[QE-users] gradients with charge compensation

[Paolo Giannozzi]

The introduction of a compensating background is needed because the energy
of a charged supercell is infinite. In the case of a charged defect, the
supercell of charged defects + compensating background will converge to the
isolated defect in the limit of large supercell, but the convergence will
be slow. Various techniques (Makov-Payne, Martyna-Tuckerman, ...) can be
used to obtain better results for reasonably-sized cells. Note that
"tot_charge=+1" means "one electron missing from the system".

I have no reason to think that forces in charged supercells are wrong (not
just approximated: wrong). Your results look strange, but it is hard to
draw any conclusion from a comparison of two very different approaches and
XC functionals. If you can provide your data, maybe we can figure out what
happens and why.

Paolo

On Wed, Apr 25, 2018 at 1:03 PM, Aleksandra Oranskaia <
aleksandra.oranskaia at kaust.edu.sa> wrote:

> Hi dear users and developers of QE,
>
> If one is interested in studying charged state defects -- is it correct to
> run supercell optimizations with a compensating jellium background ?
> Let’s say, if one is interested in +1 point defect state -- is it correct
> to add tot_charge = +1 ?
>
> I quickly checked if the gradients for molecular cation optimization are
> reasonable with such an approach. For this I took small cation with known
> structure and:
> - gaussian09-d.01 optimization with 6-11G**/B3LYP, +1 charge, 1 spin
> multiplicity gave perfectly matching structure with the real one
> - QE-6.2.1 optimization with vdw-df2/USPP and tot_charge = +1 destroyed
> the cation, it dissociated; without “jellium” the optimized structure is
> very close to the real one.
>
> I would greatly appreciate your advice on how to obtain realistic
> structures of the supercells with charged defects,
>
>
> Thanks in advance,
> Alex.
> ___
> Aleksandra Oranskaia (M.Sc.)
> ChemS PhD student, KAUST
> Phone: +966 50 1335254
>
>
>
>
>
>
>
> ------------------------------
> This message and its contents, including attachments are intended solely
> for the original recipient. If you are not the intended recipient or have
> received this message in error, please notify me immediately and delete
> this message from your computer system. Any unauthorized use or
> distribution is prohibited. Please consider the environment before printing
> this email.
> _______________________________________________
> users mailing list
> users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
>



-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20180504/435185f6/attachment.html>