[Pw_forum] ecutvcut in Hybrid functionals

[Jianpeng Liu]

Hi Layla,

Your comments are really really helpful! Thanks a lot!

best,
Jianpeng

> 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
>> -------------------------------------
>>
>> _______________________________________________
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> http://pwscf.org/mailman/listinfo/pw_forum
>>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum