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
