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<p>Dear Soumyadeep,</p>
<p><br>
</p>
<p>Your input files look fine to me.</p>
<p><br>
</p>
<p>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.</p>
<p><br>
</p>
<p>Best,</p>
<p>Iurii<br>
</p>
<p><br>
</p>
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<font size="3" face="'Times New Roman', Times, serif" color="808080">--<br>
Dr. Iurii Timrov<br>
Postdoctoral Researcher<br>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Soumyadeep <soumyadeep@rrcat.gov.in><br>
<b>Sent:</b> Thursday, September 12, 2019 2:36:00 PM<br>
<b>To:</b> Timrov Iurii<br>
<b>Cc:</b> Quantum ESPRESSO users Forum<br>
<b>Subject:</b> Re: [QE-users] hp.x code overestimates Hubbard U value</font>
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<div class="PlainText">Dear Iurii,<br>
<br>
On 12-09-2019 17:33, Timrov Iurii wrote:<br>
> Dear Soumyadeep,<br>
> <br>
> Unfortunately I cannot open the input file "LiFeAs-0GPa.scf". Could<br>
> you please share it via Google Drive or Dropbox? Is you system<br>
> magnetic, metallic?<br>
> <br>
Sorry for this I will upload it again (if problem continues please check <br>
run_hp_NCPP file). The system is non-magnetic and metallic.<br>
<br>
> The value of U is very sensitive to the type of localized functions<br>
> which are used, so we have Wannier in cRPA vs atomic/ortho-atomic in<br>
> LRT. That may make a big difference, I think.<br>
> <br>
I agreed. Since both are very different from each other.<br>
<br>
> Another aspect, comparison of methods cRPA vs constrained DFT (LRT).<br>
> There were some attempts to obtain same U with these two methods, but<br>
> nobody succeeded to so far, to the best of my knowledge. In<br>
> particular, here is an important paper concerning this issue: Phys.<br>
> Rev. B 74, 125106 (2006). In Fig. 2 of this paper you can see that<br>
> cRPA gives the value of U which is very sensitive to the fact which<br>
> electrons are allowed to screen the d-d interactions. So in your case,<br>
> I would try to understand how U was computed with cRPA (if the authors<br>
> provide enough details in the publication which you cited), i.e. which<br>
> electrons were allowed to screen. In the LRT approach instead, there<br>
> is no this kind of choice which electrons are allowed to screen: when<br>
> one perturbs e.g. d electronic states of Fe then all other electrons<br>
> in the system are allowed to screen (this is done via the<br>
> self-consistent solution of modified Kohn-Sham equations). To<br>
> conclude, comparing cRPA with LRT is not an easy task (at least I do<br>
> not know any publication which clearly makes such a comparison, apart<br>
> from the one which I mentioned above).<br>
Again you are correct. I think in cRPA they allowed only d-electrons to <br>
screen since they used them to generate wannier functions.<br>
<br>
> <br>
> Best regards,<br>
> <br>
> Iurii<br>
> <br>
> --<br>
> Dr. Iurii Timrov<br>
> Postdoctoral Researcher<br>
> <br>
> STI - IMX - THEOS and NCCR - MARVEL<br>
> <br>
> Swiss Federal Institute of Technology Lausanne (EPFL)<br>
> <br>
> CH-1015 Lausanne, Switzerland<br>
> +41 21 69 34 881<br>
> <a href="http://people.epfl.ch/265334">http://people.epfl.ch/265334</a><br>
> <br>
> -------------------------<br>
> <br>
> FROM: Soumyadeep <soumyadeep@rrcat.gov.in><br>
> SENT: Thursday, September 12, 2019 12:56:03 PM<br>
> TO: Quantum ESPRESSO users Forum<br>
> CC: Timrov Iurii<br>
> SUBJECT: Re: [QE-users] hp.x code overestimates Hubbard U value<br>
> <br>
> Dear Iurii,<br>
> Thanks you very much for the detailed explanation.<br>
> <br>
> >> ..."U" lies between 3.0-3.5 eV...<br>
> The determined value of U is calculated using cRPA method - Wannier<br>
> <br>
> function basis - Norm conserving PP's<br>
> (<a href="https://journals.jps.jp/doi/abs/10.1143/JPSJ.79.044705">https://journals.jps.jp/doi/abs/10.1143/JPSJ.79.044705</a>).<br>
> <br>
> When I do it using LRT I get almost doubled? I have checked it<br>
> w.r.t<br>
> different PP/Exchange-correlation functional here is the results,<br>
> NCPP --> 6.43, USPP --> 6.85, PBESOL --> 6.81, PAW --> 6.83<br>
> <br>
> > different oxidation states<br>
> I think oxidation state is same in both cases. Fe^2+ for Fe-besed<br>
> superconductors<br>
> <br>
> > What is important is to use U (for calculations of band<br>
> structure,<br>
> DOS, phonons, etc.) with the same parameters which which it was<br>
> computed.<br>
> Yes agreed. First of all I like to calculate it for reported values<br>
> in<br>
> literature then apply it for my calculations.<br>
> <br>
> Input files are attached (NCPP) for your consideration, that may<br>
> help<br>
> you to find out my mistakes. I am just a beginner of such calculation<br>
> and don't think without my mistake such large difference can occur<br>
> though U is not an universal parameter.<br>
> <br>
> with many thanks and best regards<br>
> Soumyadeep<br>
> <br>
> On 12-09-2019 14:35, Timrov Iurii wrote:<br>
>> Dear Soumyadeep,<br>
>> <br>
>> Hubbard U is not a universal parameter. If you compute Hubbard U<br>
> from<br>
>> first principles, e.g. using linear response theory (LRT) [PRB 71,<br>
>> 035105 (2005); PRB 98, 085127 (2018)] then the value of U depends on<br>
>> many factors:<br>
>> <br>
>> - Manifold of localized functions (atomic, ortho-atomic, Wannier,<br>
>> etc.);<br>
>> <br>
>> - Pseudopotentials;<br>
>> <br>
>> - Oxidation state;<br>
>> <br>
>> - Exchange-correlation functional (LDA, PBE, PBEsol, etc.);<br>
>> <br>
>> - Environment (e.g. U for Mn-3d in MnO and BiMnO3 is not exactly the<br>
>> same).<br>
>> <br>
>> For example, check the paper by H. Kulik and N. Marzari, J. Chem.<br>
>> Phys. 129, 134314 (2008). In particular, check the appendix in this<br>
>> paper, and you will see that U is very sensitive to the oxidation<br>
>> state.<br>
>> <br>
>> Another aspect is whether U was computed in "one-shot" or<br>
>> "self-consistently". If you want to learn more about the<br>
>> self-consistent U, I recommend these papers: H. Hsu et al., PRB 79,<br>
>> 125124 (2009); C. Ricca et al., PRB 99, 094102 (2019); M. Cococcioni<br>
>> and N. Marzari, PRM 3, 033801 (2019).<br>
>> <br>
>>> ..."U" lies between 3.0-3.5 eV...<br>
>> <br>
>> Where do these values come from? Are they empirical? Or were they<br>
>> computed with cRPA? Please note that comparing U is not very<br>
>> meaningful (in my understanding), especially if you do not specify<br>
> how<br>
>> it was determined. As I wrote above, the value of U computed from<br>
>> first principles depends on many factors. So if you compute it using<br>
>> different methods (LRT vs cRPA), different localized functions<br>
> (atomic<br>
>> vs Wannier), different oxidation states, etc. then you will not get<br>
>> the same U. What is important is to use U (for calculations of band<br>
>> structure, DOS, phonons, etc.) with the same parameters which which<br>
> it<br>
>> was computed.<br>
>> <br>
>> I recommend to have a look at the hands-on about calculation of U<br>
>> using Quantum ESPRESSO (hp.x code):<br>
>> <br>
>> <a href="https://agenda.ethernet.edu.et/event/33/">https://agenda.ethernet.edu.et/event/33/</a><br>
>> <br>
>> Hope this helps! If something is not precise in my explanations, it<br>
>> would great if other experts correct me.<br>
>> <br>
>> Best regards,<br>
>> <br>
>> Iurii<br>
>> <br>
>> --<br>
>> Dr. Iurii Timrov<br>
>> Postdoctoral Researcher<br>
>> <br>
>> STI - IMX - THEOS and NCCR - MARVEL<br>
>> <br>
>> Swiss Federal Institute of Technology Lausanne (EPFL)<br>
>> <br>
>> CH-1015 Lausanne, Switzerland<br>
>> +41 21 69 34 881<br>
>> <a href="http://people.epfl.ch/265334">http://people.epfl.ch/265334</a><br>
>> <br>
>> -------------------------<br>
>> <br>
>> FROM: users <users-bounces@lists.quantum-espresso.org> on behalf of<br>
>> Soumyadeep <soumyadeep@rrcat.gov.in><br>
>> SENT: Wednesday, September 11, 2019 4:35:37 PM<br>
>> TO: Users<br>
>> SUBJECT: [QE-users] hp.x code overestimates Hubbard U value<br>
>> <br>
>> Dear QE users,<br>
>> <br>
>> I am getting a overestimated value of Hubbard parameters using<br>
> hp.x<br>
>> <br>
>> executable of Quantum Espresso. My material is iron based<br>
>> superconductors (LiFeAs) for which "U" lies between 3.0-3.5 eV, but<br>
>> using this code I get it around 6.4-6.5 eV.<br>
>> <br>
>> Can anyone find out possible mistakes?<br>
>> <br>
>> with many thanks and best regards<br>
>> Soumyadeep<br>
>> -------------------------------------------------------------------<br>
>> Soumyadeep Ghosh,<br>
>> Senior Research Fellow,<br>
>> Homi Bhabha National Institute (HBNI),<br>
>> Raja Ramanna Centre for Advanced Technology, Indore, India-452013<br>
>> Mob: (+91)9424664553<br>
>> User Lab: 0731244-2580<br>
>> Email: soumyadeepghosh35@gmail.com, soumyadeep@rrcat.gov.in<br>
>> -------------------------------------------------------------------<br>
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