[Pw_forum] ecutvcut in Hybrid functionals
Dear Amin, ecutvcut is ignored is exxdiv_treatment is different from vcut_ws. Which is the case by default. We leave this variable there only because you could have chosen to set exxdiv_treatment="ecut_ws", and in this case (and ONLY in this case) you need a reasonable value for ecutvcut. cheers Layla 2012/11/23 Amin Torabi > Dear Layla > > You said that "ecutvcut is a parameter which is not strictly bonded to > hybrid functional parameters, but to strongly anisotropic supercells" > So, why do we have ecutvcut=0.7 in the PBE0 example for bulk Si? > > > > > On Fri, Nov 23, 2012 at 2:31 AM, Layla Martin-Samos < > lmartinsamos at gmail.com> wrote: > >> Dear Leonardo and Jianpeng, the "issue" is that HSE contain only the >> shortrange part of coulomb potential for the fock term (thas why HSE >> contain an exponential with a screening lenght). Ecutvcut, spehrical cutoff >> and all similar tricks APPLY ONLY for the "REAL" Coulomb potential, the >> FULL Coulomb potential. So, one has to be very careful when dealing with >> hybrids that do not contain the full coulomb potential. >> > > > > -- > *** > Amin Torabi > Ph.D. Student > Chemistry Dept. > Western University > London, On Canada, N6A 5B7 > Phone: 519-661-2111 Ext: 87871 > > > > ___ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -- next part -- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121126/0f8fa952/attachment.html
[Pw_forum] ecutvcut in Hybrid functionals
On Fri, 23 Nov 2012 17:41:19 +0100, Amin Torabi wrote: > Dear Layla > > You said that "ecutvcut is a parameter which is not strictly bonded to > hybrid functional parameters, but to strongly anisotropic supercells" > So, why do we have ecutvcut=0.7 in the PBE0 example for bulk Si? > > Hmm I think there seems to be a lot of confusion here. The first thing to understand is that the value ecutvcut has no effect if exxdiv_treatment is set to anything other than 'vcut_ws'. By default all of the EXX examples run with exxdiv_treatment set to 'gygi-baldereschi'. So in all these examples the value of ecutvcut is redundant. However with extra command line options to run_example it is possible to run the examples with different exxdiv_treatment values. Hence why ecutvcut is set to some default value (0.7) In the case of HSE however using vcut_ws (or vcut_spherical) is a rather dubious thing to do at best (due to the fact the functional already separates the exchange interaction into long and short range and only uses true non-local exchange in the short range part.) As for the meaning of ecutvcut: vcut_ws truncates the Coulomb potential *used in the exact-exchange integrals* in real space according to the extent of the Wigner-Seitz cell (taking into accoutn k-point sampling). The way it does this is by building the interaction on a real space grid and the fourier transforming it, right at the start of the calculation. This interaction (no in G space) is used throughout the rest of the calculation for the EXX terms. ecutvcut is the cutoff used in this transform and has to strike a balance between producing an accurate enough 1/|r-r'| function in G space and being so large as to take up too much time at the start of the calculation. Brgds Simon -- Simon Binnie | Post Doc, Condensed Matter Sector Scuola Internazionale di Studi Avanzati (SISSA) Via Bonomea 256 | 34100 Trieste | sbinnie at sissa.it
[Pw_forum] ecutvcut in Hybrid functionals
Dear Layla You said that "ecutvcut is a parameter which is not strictly bonded to hybrid functional parameters, but to strongly anisotropic supercells" So, why do we have ecutvcut=0.7 in the PBE0 example for bulk Si? On Fri, Nov 23, 2012 at 2:31 AM, Layla Martin-Samos wrote: > Dear Leonardo and Jianpeng, the "issue" is that HSE contain only the > shortrange part of coulomb potential for the fock term (thas why HSE > contain an exponential with a screening lenght). Ecutvcut, spehrical cutoff > and all similar tricks APPLY ONLY for the "REAL" Coulomb potential, the > FULL Coulomb potential. So, one has to be very careful when dealing with > hybrids that do not contain the full coulomb potential. > -- *** Amin Torabi Ph.D. Student Chemistry Dept. Western University London, On Canada, N6A 5B7 Phone: 519-661-2111 Ext: 87871 -- next part -- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121123/0cdea41d/attachment.html
[Pw_forum] ecutvcut in Hybrid functionals
Dear Leonardo and Jianpeng, the "issue" is that HSE contain only the shortrange part of coulomb potential for the fock term (thas why HSE contain an exponential with a screening lenght). Ecutvcut, spehrical cutoff and all similar tricks APPLY ONLY for the "REAL" Coulomb potential, the FULL Coulomb potential. So, one has to be very careful when dealing with hybrids that do not contain the full coulomb potential. cheers Layla 2012/11/23 Jianpeng Liu > 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 > > 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 > >> > > >> >> 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 > > > ___ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -- next part -- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121123/c4a4e274/attachment-0001.html
[Pw_forum] ecutvcut in Hybrid functionals
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 > 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 >> > >> >> 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
[Pw_forum] ecutvcut in Hybrid functionals
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 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 > > > >> 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 > -- next part -- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121122/c48721dd/attachment.html
[Pw_forum] ecutvcut in Hybrid functionals
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 > 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 > -- next part -- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121120/3bcedad4/attachment.html
[Pw_forum] ecutvcut in Hybrid functionals
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 > >> 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] ecutvcut in Hybrid functionals
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 -
