[QE-users] Regarding input file for hp.x

[Timrov Iurii]

Dear Mohaddeseh,


> 1. In the NiO examples in the HP folder, there are two Ni atoms, namely NI1 and Ni2. Fortunately, hubbard parameters are obtained the same for both. But for my structure Ti1 and Ti2 and Ti3 have different u values.

If you obtain different U values for Ti1, Ti2, and Ti3, then these species are inequivalent and this is OK. If they were equivalent, you would obtain same U for all of them like in the example for NiO.

> in all of the literature just one U is reported for the metallic element. Is it OK to report 3 different U values by linear response method or not?

I presume that in the literature, empirical U was used - in this case it is hard (or maybe even impossible) to find different U for different inequivalent species. But with ab initio methods this comes out naturally from the linear response of the system. And yes, it is OK to report 3 different U, provided that you are sure that this is correct (i.e. that you indeed have three inequivalent species) and that you explain in your paper that you computed U from first principles that allows you to have site-depend U.

You might be interested checking these references about site-dependent U:
- C. Ricca, I. Timrov, M. Cococcioni, N. Marzari, and U. Aschauer, Phys. Rev. B 99, 094102 (2019).
- C. Ricca, I. Timrov, M. Cococcioni, N. Marzari, and U. Aschauer, Phys. Rev. Research 2, 023313 (2020).


> 2. Is it necessary to relax the structure before starting the calculation of U parameters by linear response? In fact, the obtained U values from relax calculation and without relaxation are totally different with each other.


It depends what you want to do. U can be computed in two ways: 1) "one-shot", or 2) self-consistently. In the first case, one computes U for a given geometry and that's it. In the second case, U is computed for a given geometry, then vc-relax is done using DFT+U (with U computed in the first step), then U is recomputed from the new geometry, and so on until both the geometry and U do not change (within specified thresholds). In general, the second option should be used. But if you want to compute U for a fixed geometry for some reason (e.g. for the experimental geometry, like here: I. Timrov et al., Phys. Rev. Research 2, 033265 (2020)), then use the first option. If you want to read more about this, check two references above (C. Ricca et al.) and this one: M. Cococcioni and N. Marzari, Phys. Rev. Materials 3, 033801 (2019). Last, we are preparing a manuscript with detailed explanations about the self-consistent calculation of Hubbard parameters.

Cheers,
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-bounces at lists.quantum-espresso.org> on behalf of Mohad Abbasnejad <mohaddeseh.abbasnejad at gmail.com>
Sent: Friday, August 28, 2020 5:32:46 PM
To: Quantum ESPRESSO users Forum
Subject: [QE-users] Regarding input file for hp.x

Hello QE users
There are two basic questions for preparing input files for hp.x
1. In the NiO examples in the HP folder, there are two Ni atoms, namely NI1 and Ni2. Fortunately, hubbard parameters are obtained the same for both. But for my structure Ti1 and Ti2 and Ti3 have different u values. in all of the literature just one U is reported for the metallic element. Is it OK to report 3 different U values by linear response method or not?

2. Is it necessary to relax the structure before starting the calculation of U parameters by linear response? In fact, the obtained U values from relax calculation and without relaxation are totally different with each other.

Any help would be appreciated.

Regards,
Mohaddeseh
--
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Mohaddeseh Abbasnejad,
Assistant Professor of Physics,
Faculty of Physics,
Shahid Bahonar University of Kerman,
Kerman, Iran
P.O. Box 76169-133
Tel: +98 34 31322199
Fax: +98 34 33257434
Cellphone: +98 917 731 7514
E-Mail:     mohaddeseh.abbasnejad at gmail.com<mailto:mohaddeseh.abbasnejad at gmail.com>
Website:  academicstaff.uk.ac.ir/moabbasnejad<http://academicstaff.uk.ac.ir/moabbasnejad>
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