[Pw_forum] ecutvcut in Hybrid functionals

[Layla Martin-Samos]

Dear Jianpeng, ecutvcut is a parameter which is not strictly bonded to
hybrid functional parameters, but to strongly anisotropic supercells like
in the case of quasi 1D systems and fock like operators. I will be more
precise. If you have an hybrid functional AND you want to have the
electronic properties of a polymer chain or a nanotube, i.e. if you
multiply the cell parameter by the number of kpoint in each direction then
you obtain an effective supercell which is anisotropic (like 6*6*50), then
to avoid divergencies for small q vectors in the integration of the fock
operator, one has to turn on exxdiv_treatment="vcut_ws" and ecutvcut=1.2 or
something appropriate (you need to converge with this value). vcut_ws
applies a real space cutoff in the wigner Seitz cell of your supercell
until a reciprocal space cutoff of ecutvcut. The more is your cell
anisotropic bigger has to be ecutvcut. If you are dealing with bulk
materials, you do not have to care about this!!!

hope it helps cheers

Layla

2012/11/19 Jianpeng Liu <jpliu at physics.rutgers.edu>

> Dear QE users and developers,
>
> I am doing hybrid-functional calculations, and I am confused about the
> setting of ecutvcut. In the examples of Si, for pbe0-type hybrid
> functional, the ecutvcut is set to be 0.7Ry, while for hse-type hybrid
> functional with a screened Coulomb potential, ecutvcut is just set as
> default which is 0.0Ry. Could anyone explain why? For a typical
> semiconductor with s or p valence orbitals, what kind of ecutvcut value is
> recommended?
>
> Thanks a lot.
>
> best,
> Jianpeng Liu
>
> -------------------------------------
> Ph.D. candidate,
> Department of physics and astronomy,
> Rutgers University
> -------------------------------------
>
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