[Pw_forum] problem hybrid pseudopotential calculations

Josue Itsman Clavijo Penagos jiclavijop at unal.edu.co
Fri Jul 22 19:09:16 CEST 2016

Dear, Muhammad Adnan Saqlain, remember the user documentation for

Specific for EXX. It selects the kind of approach to be used
for treating the Coulomb potential divergencies at small q vectors.

gygi-baldereschi : appropriate for cubic and *quasi-cubic supercells*
vcut_spherical : appropriate for cubic and quasi-cubic supercells
vcut_ws : appropriate for strongly anisotropic supercells, see also
none : sets Coulomb potential at G,q=0 to 0.0 (required for GAU-PBE)

*Besides that, *I have some observations and suggestions for you based in
the input file you send, so you can realize why does QE is failing when
trying to simulate your system:

1 - Check if you really need to apply smearing, since this technique is
intended to be useful for metallic systems, and Anatase is cleary not a
metallic system, in fact, is more a Wide-gap or Insulator -type system.

2 - You do want to perform a vc-relax calculation, but nothing are
specified in the cards &IONS and &CELL. There is not cell relaxing
algorithm specified (BFGS? MD?)

3 - The card &ATOMIC_POSITIONS shows nothing: No atoms, no cell to relax.

4 - In the card &SYSTEM , *ecutwfc = 40.* This, in my humble opinion, a
very poor cutoff for a serious calculation. Do a ecutwfc convergence test
before attempt your system.

5 - Please take in account that a hybrid calculation is VERY expensive in
terms of computational demand, so if you set up a vc-relax calculation
using hybrid PPS you must test if *nqx1 = 1, 2 or 3 really makes a

*6 - For some systems, input_dft=HSE is faster than **input_dft = "PBE0".
Check if that could be your case.*

By the way, are you sure Anatase has a cubic crystal structure? Does
XCrysden show the correct structure for your input?

*Best regards, *

Josué Clavijo, PhD.
Assistant Professor
Universidad Nacional de Colombia
Departamento de Química
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