[Pw_forum] problem hybrid pseudopotential calculations

[Josue Itsman Clavijo Penagos]

Dear, Muhammad Adnan Saqlain, remember the user documentation for
*exxdiv_treatment*:

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
          ecutvcut.
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
difference.*

*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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