Dear Soumyadeep,
Your input files look fine to me. I would try to compute U in a self-consistent way. Just take the value you got from a one-shot calculation and plug it in the SCF input and then redo the HP calculation. Repeat this procedure until U does not change any longer. On top of that, you may perform a relaxation of the structure. By doing so, you will obtain U and the structure which are consistent with each other. More about this is discussed in the papers which I mentioned in my previous email. Best, 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: Soumyadeep <soumyad...@rrcat.gov.in> Sent: Thursday, September 12, 2019 2:36:00 PM To: Timrov Iurii Cc: Quantum ESPRESSO users Forum Subject: Re: [QE-users] hp.x code overestimates Hubbard U value Dear Iurii, On 12-09-2019 17:33, Timrov Iurii wrote: > Dear Soumyadeep, > > Unfortunately I cannot open the input file "LiFeAs-0GPa.scf". Could > you please share it via Google Drive or Dropbox? Is you system > magnetic, metallic? > Sorry for this I will upload it again (if problem continues please check run_hp_NCPP file). The system is non-magnetic and metallic. > The value of U is very sensitive to the type of localized functions > which are used, so we have Wannier in cRPA vs atomic/ortho-atomic in > LRT. That may make a big difference, I think. > I agreed. Since both are very different from each other. > Another aspect, comparison of methods cRPA vs constrained DFT (LRT). > There were some attempts to obtain same U with these two methods, but > nobody succeeded to so far, to the best of my knowledge. In > particular, here is an important paper concerning this issue: Phys. > Rev. B 74, 125106 (2006). In Fig. 2 of this paper you can see that > cRPA gives the value of U which is very sensitive to the fact which > electrons are allowed to screen the d-d interactions. So in your case, > I would try to understand how U was computed with cRPA (if the authors > provide enough details in the publication which you cited), i.e. which > electrons were allowed to screen. In the LRT approach instead, there > is no this kind of choice which electrons are allowed to screen: when > one perturbs e.g. d electronic states of Fe then all other electrons > in the system are allowed to screen (this is done via the > self-consistent solution of modified Kohn-Sham equations). To > conclude, comparing cRPA with LRT is not an easy task (at least I do > not know any publication which clearly makes such a comparison, apart > from the one which I mentioned above). Again you are correct. I think in cRPA they allowed only d-electrons to screen since they used them to generate wannier functions. > > Best regards, > > 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: Soumyadeep <soumyad...@rrcat.gov.in> > SENT: Thursday, September 12, 2019 12:56:03 PM > TO: Quantum ESPRESSO users Forum > CC: Timrov Iurii > SUBJECT: Re: [QE-users] hp.x code overestimates Hubbard U value > > Dear Iurii, > Thanks you very much for the detailed explanation. > > >> ..."U" lies between 3.0-3.5 eV... > The determined value of U is calculated using cRPA method - Wannier > > function basis - Norm conserving PP's > (https://journals.jps.jp/doi/abs/10.1143/JPSJ.79.044705). > > When I do it using LRT I get almost doubled? I have checked it > w.r.t > different PP/Exchange-correlation functional here is the results, > NCPP --> 6.43, USPP --> 6.85, PBESOL --> 6.81, PAW --> 6.83 > > > different oxidation states > I think oxidation state is same in both cases. Fe^2+ for Fe-besed > superconductors > > > What is important is to use U (for calculations of band > structure, > DOS, phonons, etc.) with the same parameters which which it was > computed. > Yes agreed. First of all I like to calculate it for reported values > in > literature then apply it for my calculations. > > Input files are attached (NCPP) for your consideration, that may > help > you to find out my mistakes. I am just a beginner of such calculation > and don't think without my mistake such large difference can occur > though U is not an universal parameter. > > with many thanks and best regards > Soumyadeep > > On 12-09-2019 14:35, Timrov Iurii wrote: >> Dear Soumyadeep, >> >> Hubbard U is not a universal parameter. If you compute Hubbard U > from >> first principles, e.g. using linear response theory (LRT) [PRB 71, >> 035105 (2005); PRB 98, 085127 (2018)] then the value of U depends on >> many factors: >> >> - Manifold of localized functions (atomic, ortho-atomic, Wannier, >> etc.); >> >> - Pseudopotentials; >> >> - Oxidation state; >> >> - Exchange-correlation functional (LDA, PBE, PBEsol, etc.); >> >> - Environment (e.g. U for Mn-3d in MnO and BiMnO3 is not exactly the >> same). >> >> For example, check the paper by H. Kulik and N. Marzari, J. Chem. >> Phys. 129, 134314 (2008). In particular, check the appendix in this >> paper, and you will see that U is very sensitive to the oxidation >> state. >> >> Another aspect is whether U was computed in "one-shot" or >> "self-consistently". If you want to learn more about the >> self-consistent U, I recommend these papers: H. Hsu et al., PRB 79, >> 125124 (2009); C. Ricca et al., PRB 99, 094102 (2019); M. Cococcioni >> and N. Marzari, PRM 3, 033801 (2019). >> >>> ..."U" lies between 3.0-3.5 eV... >> >> Where do these values come from? Are they empirical? Or were they >> computed with cRPA? Please note that comparing U is not very >> meaningful (in my understanding), especially if you do not specify > how >> it was determined. As I wrote above, the value of U computed from >> first principles depends on many factors. So if you compute it using >> different methods (LRT vs cRPA), different localized functions > (atomic >> vs Wannier), different oxidation states, etc. then you will not get >> the same U. What is important is to use U (for calculations of band >> structure, DOS, phonons, etc.) with the same parameters which which > it >> was computed. >> >> I recommend to have a look at the hands-on about calculation of U >> using Quantum ESPRESSO (hp.x code): >> >> https://agenda.ethernet.edu.et/event/33/ >> >> Hope this helps! If something is not precise in my explanations, it >> would great if other experts correct me. >> >> Best regards, >> >> 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 <users-boun...@lists.quantum-espresso.org> on behalf of >> Soumyadeep <soumyad...@rrcat.gov.in> >> SENT: Wednesday, September 11, 2019 4:35:37 PM >> TO: Users >> SUBJECT: [QE-users] hp.x code overestimates Hubbard U value >> >> Dear QE users, >> >> I am getting a overestimated value of Hubbard parameters using > hp.x >> >> executable of Quantum Espresso. My material is iron based >> superconductors (LiFeAs) for which "U" lies between 3.0-3.5 eV, but >> using this code I get it around 6.4-6.5 eV. >> >> Can anyone find out possible mistakes? >> >> with many thanks and best regards >> Soumyadeep >> ------------------------------------------------------------------- >> Soumyadeep Ghosh, >> Senior Research Fellow, >> Homi Bhabha National Institute (HBNI), >> Raja Ramanna Centre for Advanced Technology, Indore, India-452013 >> Mob: (+91)9424664553 >> User Lab: 0731244-2580 >> Email: soumyadeepghos...@gmail.com, soumyad...@rrcat.gov.in >> ------------------------------------------------------------------- >> _______________________________________________ >> Quantum ESPRESSO is supported by MaX >> ( [1]www.max-centre.eu/quantum-espresso [1]) >> users mailing list users@lists.quantum-espresso.org >> https://lists.quantum-espresso.org/mailman/listinfo/users >> >> >> Links: >> ------ >> [1] http://www.max-centre.eu/quantum-espresso >> _______________________________________________ >> Quantum ESPRESSO is supported by MaX >> (<http://>www.max-centre.eu/quantum-espresso [2]) >> users mailing list users@lists.quantum-espresso.org >> https://lists.quantum-espresso.org/mailman/listinfo/users > > > Links: > ------ > [1] http:// > [2] http://www.max-centre.eu/quantum-espresso
_______________________________________________ Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso) users mailing list users@lists.quantum-espresso.org https://lists.quantum-espresso.org/mailman/listinfo/users
