Hello All, Thank you very much. Giuseppe: Thanks for clarifying. You have suggested me to use turbo.x for absorption spectrum over epsilon.x for periodic systems, while ago. I do remember now. Thanks Manu (McMaster University)
On Wed, Apr 8, 2020 at 2:21 PM Michal Krompiec <[email protected]> wrote: > Dear All, > Thank you very much, this explains that it can't be done for my system > and closes the case for now :(. It would be great if someone > implemented the missing term for hybrids in [H,x]. > Best, > Michal > > On Wed, 8 Apr 2020 at 19:15, Timrov Iurii <[email protected]> wrote: > > > > Dear All, > > > > > > > Do I remember correctly that epsilon.x also does not take into account > the nonlocal pseudopotential contribution? > > > > > > Correct > > > > > > > ...there used to be an option in the turbo_davidson.x and > turbo_lanczos.x codes, namely no_hxc=.true., which permits an > independent-electron calculation. > > > > > > Correct. By default, the matrix element of the dipole operator is > computed (in reciprocal space) via the matrix element of the commutator > that Paolo mentioned [H,x] (see Eq.(14) in S. Baroni and R. Resta, Phys. > Rev. B 33, 7017 (1986)): but in this case there is a kinetic term and the > part coming from the non-local part of a pseudopotential. In epsilon.x, > only the kinetic term is present, while in TDDFT codes both terms are > present (the second term was implement long ago in the Phonon code to > compute the dielectric tensor). But still, in the case of hybrid > functionals, in [H,x] there is another term which is missing - the > commutator with another non-local potential which is EXX. Stefano Baroni > and I developed a way how to compute this missing term several years ago: I > implemented it in QE and it worked well, but I never had time to release it > and publish some paper about it. But there is a workaround for finite > systems: the matrix element of the dipole operator can be comput > ed in re > al space based on the observation that the charge density of the finite > system decays fast outside the finite system, and hence the non-periodicity > problem of the dipole operator is no longer a problem. But this trick in > real space is not gonna work for periodic systems, because the charge > density if non-zero in the whole simulation cell. Thus, the only way to > overcome this problem is to implement the missing term for hybrids in [H,x]. > > > > > > Greetings, > > > > Iurii > > > > > > -- > > Dr. Iurii Timrov > > Postdoctoral Researcher > > STI - IMX - THEOS and NCCR - MARVEL > > Swiss Federal Institute of Technology Lausanne (EPFL) > > CH-1015 Lausanne, Switzerland > > +41 21 69 34 881 > > http://people.epfl.ch/265334 > > ________________________________ > > From: users <[email protected]> on behalf of > Giuseppe Mattioli <[email protected]> > > Sent: Wednesday, April 8, 2020 7:42:35 PM > > To: Quantum ESPRESSO users Forum > > Subject: Re: [QE-users] epsilon.x and hybrids > > > > > > Dear all > > I don't want to raise the confusion level, so please correct me if I'm > > wrong... If you want to calculate a heavily approximate absorption > > spectrum of a (large and non-symmetrical) periodic system after a > > ground state hybrid calculation, there used to be an option in the > > turbo_davidson.x and turbo_lanczos.x codes, namely no_hxc=.true., > > which permits an independent-electron calculation. At least, hybrid > > functionals and Gamma ground states should be properly treated by such > > codes, resulting in an absorption spectrum compatible with those > > obtained by using epsilon.x, which, AFAIK, calculates > > <occupied|r|virtual> contributions to the absorption spectrum. > > However, I don't know how much this kind of calculation is expensive > > for large supercells. Of course if you are not interested in > > absorption, then my suggestion is nonsense... > > HTH > > Giuseppe > > > > Quoting Lorenzo Paulatto <[email protected]>: > > > > > Also, epsilon.x cannot use symmetry-reduced grids, which would be a > > > huge wast of time with hybrids, but you can use open_grid.x after > > > the pw.x calculation too obtain the full grid and work around this > > > problem. > > > > > > cheers > > > > > > On 4/8/20 6:38 PM, Paolo Giannozzi wrote: > > >> I think epsilon.x assumes that the dipole element of x can be > > >> computed using [H,x]=p\hbar/m. The exchange potential is nonlocal, > > >> so its commutator with x will yield an additional term that is not > > >> accounted for. Not sure how important it is in practice. Do I > > >> remember correctly that epsilon.x also does not take into account > > >> the nonlocal pseudopotential contribution? > > >> > > >> Paolo > > >> > > >> On Wed, Apr 8, 2020 at 4:29 PM Manu Hegde <[email protected] > > >> <mailto:[email protected]>> wrote: > > >> > > >> Hi Michal, > > >> Yes, it is possible.I did use both supercell and hybrid > > >> calculations. It did work. > > >> Manu > > >> > > >> On Wed, Apr 8, 2020 at 10:08 AM Michal Krompiec > > >> <[email protected] <mailto:[email protected]>> > wrote: > > >> > > >> Hello, > > >> Is it possible to use epsilon.x on results of a calculation > with a > > >> hybrid functional (supercell, gamma point only)? > > >> > > >> Thanks, > > >> > > >> Michal Krompiec > > >> Merck KGaA > > >> _______________________________________________ > > >> Quantum ESPRESSO is supported by MaX > > >> (www.max-centre.eu/quantum-espresso > > >> <http://www.max-centre.eu/quantum-espresso>) > > >> users mailing list [email protected] > > >> <mailto:[email protected]> > > >> https://lists.quantum-espresso.org/mailman/listinfo/users > > >> > > >> _______________________________________________ > > >> Quantum ESPRESSO is supported by MaX > > >> (www.max-centre.eu/quantum-espresso > > >> <http://www.max-centre.eu/quantum-espresso>) > > >> users mailing list [email protected] > > >> <mailto:[email protected]> > > >> https://lists.quantum-espresso.org/mailman/listinfo/users > > >> > > >> > > >> > > >> -- > > >> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche, > > >> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy > > >> Phone +39-0432-558216, fax +39-0432-558222 > > >> > > >> > > >> _______________________________________________ > > >> Quantum ESPRESSO is supported by MaX ( > www.max-centre.eu/quantum-espresso) > > >> users mailing list [email protected] > > >> https://lists.quantum-espresso.org/mailman/listinfo/users > > >> > > > > > > -- > > > Lorenzo Paulatto - Paris > > > _______________________________________________ > > > Quantum ESPRESSO is supported by MaX ( > www.max-centre.eu/quantum-espresso) > > > users mailing list [email protected] > > > https://lists.quantum-espresso.org/mailman/listinfo/users > > > > > > > > GIUSEPPE MATTIOLI > > CNR - ISTITUTO DI STRUTTURA DELLA MATERIA > > Via Salaria Km 29,300 - C.P. 10 > > I-00015 - Monterotondo Scalo (RM) > > Mob (*preferred*) +39 373 7305625 > > Tel + 39 06 90672342 - Fax +39 06 90672316 > > E-mail: <[email protected]> > > > > _______________________________________________ > > Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso > ) > > users mailing list [email protected] > > https://lists.quantum-espresso.org/mailman/listinfo/users > > _______________________________________________ > > Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso > ) > > users mailing list [email protected] > > https://lists.quantum-espresso.org/mailman/listinfo/users > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso) > users mailing list [email protected] > https://lists.quantum-espresso.org/mailman/listinfo/users >
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