<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:12pt"><pre style="font-family: arial,helvetica,sans-serif;"><i>Dear pwscf users,<br>I performed some calculations by using PBE0 and HSE on the ZnO system. When I used a supercell with 4 atoms , <br>I obtained a Fermi levels comparable to those calculate without hybrid functional (Ef= 7.68 eV) .<br> Almost, the same result is obtained for a supercell with 16 atoms.<br> But (for a supercell with 16 atoms) with PBE0 and HSE Ef becomes large (Ef~28,258 eV).<br> <br>Why such a problem occurs?<br> Thanks a lot in advance</i><i><br>Mourad<br></i></pre><div> </div><div>DEBBICHI Mourad<br>Unité de Recherche Physique des Solides,99/UR/13-19,<br>Département de Physique, Faculté des Science de Monastir,<br>Avenue de l'Environnement 5019, Monastir Tunisie.<br>tél:+21697487042<br>mourad_fsm@yahoo.fr</div></div></body></html>