Hi Leonardo, I really do not know about this. For security, I followed the example and set ecutvcut to be zero for a HSE hybrid functional.
best, Jianpeng > HSE is "a PBE0 with a cutoff". I don't know if it has been fixed, but some > time ago ecutvcut interfered with that cutoff, making HSE behave just as > PBE0 (i.e., when ecutvcut was on, calculations done with HSE and PBE0 gave > the same results). > Maybe that's why in the examples with HSE was used ecutvcut=0.0. I just > don't know if this is still happening, or if the bug was fixed and just > the > example that wasn't updated. > > Leonardo Jorge > PhD Student at USP - Brazil > Nanomol Group > http://nanomol.if.usp.br > > On Tue, Nov 20, 2012 at 10:48 AM, Jianpeng Liu > <jpliu at physics.rutgers.edu>wrote: > >> 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 >> >> >> _______________________________________________ >> 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
