[Pw_forum] HSE&PBE0 problem

[Layla Martin-Samos]

Dear mourad, in principle the exact exchange term is longer ranged than
traditional DFT functionals. In any case you should converge your
calculations with respect to the system size (or the kpoints and nqx1, nqx2
and nqx3 points). In the particular case of HSE, the screening parameter
assumes a decay within the supercell (fixed from input). If the supercell
is no big enough you could see strong oscillations with respect to the cell
dimension for small cells. Look at the bibliography for more information.

best regards

Layla

2012/5/7 debbichi mourad <mourad_fsm at yahoo.fr>

>
> Dear pwscf users,
>
> *I performed some calculations by using PBE0 and HSE on the ZnO system. When I used a supercell with 4 atoms ,
> I obtained a Fermi levels comparable to those calculate without  hybrid functional (Ef= 7.68 eV) .
>  Almost, the same result is obtained for a supercell with 16 atoms.
>  But (for a supercell with 16 atoms) with PBE0 and HSE Ef becomes large (Ef~28,258 eV).
>
> Why such a problem occurs?
>  Thanks a lot  in
>  advance**
> Mourad
> *
>
>
> DEBBICHI Mourad
> Unité de Recherche Physique des Solides,99/UR/13-19,
> Département de Physique, Faculté des Science de Monastir,
> Avenue de l'Environnement 5019, Monastir Tunisie.
> tél:+21697487042
> mourad_fsm at yahoo.fr
>
>
>
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