[QE-users] DFT+U calculation and Hubbard_J0 parameter

[Timrov Iurii]

Dear Yuvam,


> I wanted to know how do I know in what orbital how much U parameter I should provide.

You can compute U from first principles using the hp.x code which is a part of Quantum ESPRESSO.

> In QE, there's only one option of Hubbard_U and not any orbital specific data. But in other programs like SIESTA, I had to put U and J value for each orbital, 3d and 4s in case of Cr.

In QE there is a multichannel implementation for DFT+U, but it is still experimental. You can find some examples in q-e/test-suite/pw_lda+U.

> Suppose I used U=5 in QE, how should I know what value should I use for SIESTA?

The value of U is not transferable from one code to another. U depends on many factors (Hubbard manifold, pseudopotentials, functional, etc.). Have a look here:
http://theossrv1.epfl.ch/Main/DFTHubbard

> If I use U=5 for 3d in SIESTA, what should I use for 4s as it is also one of the outermost orbitals.


Applying the U correction to s-type orbitals is questionable. Typically the U correction is applied to the orbitals of the d and f type. Sometimes people put U also on p-type orbitals, but there is also no general consensus about this.


U=5 for 3d in SIESTA, does not mean that you will have U=5 for 3d in QE (see my comment above). Just compute it using hp.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 <users-bounces at lists.quantum-espresso.org> on behalf of Yuvam Bhateja <yuvamb16 at gmail.com>
Sent: Thursday, October 29, 2020 1:58:44 PM
To: Quantum ESPRESSO users Forum
Subject: Re: [QE-users] DFT+U calculation and Hubbard_J0 parameter

Thank you very much for this valuable information.

I wanted to know how do I know in what orbital how much U parameter I should provide.
In QE, there's only one option of Hubbard_U and not any orbital specific data. But in other programs like SIESTA, I had to put U and J value for each orbital, 3d and 4s in case of Cr.
Suppose I used U=5 in QE, how should I know what value should I use for SIESTA?
If I use U=5 for 3d in SIESTA, what should I use for 4s as it is also one of the outermost orbitals.

Regards
Yuvam


On Wed, 28 Oct 2020, 5:03 pm Matteo Cococcioni, <matteo.cococcioni at unipv.it<mailto:matteo.cococcioni at unipv.it>> wrote:

Dear Yuvam

please see below.


Il giorno mer 28 ott 2020 alle ore 10:58 Yuvam Bhateja <yuvamb16 at gmail.com<mailto:yuvamb16 at gmail.com>> ha scritto:
Hello experts,

I have been using Quantum ESPRESSO for my project and now I wanted to include DFT+U in my calculation.

I was using lda_plus_u_kind = 0 (which only uses Hubbard_U parameter) along with Hubbard_J0.
For example-

lda_plus_u_kind=0
Hubbard_U(1)=5.0
Hubbard_J0(1)=0.48

Using the above configuration my system converged perfectly.

I wanted to know if I am doing something wrong here? Will the value of Hubbard_J0 be even considered if I am using lda_plus_u_kind=0?


why do you think there is something wrong?
In order to understand whether J0 makes any difference just try without it and compare the results.



I wished to replicate the results in other softwares like SIESTA which only uses rotationally invariant scheme (i.e., equivalent to lda_plus_u=1).
Can I use values of U=5.0 and J=0.48 as mentioned above in other DFT codes?

strictly speaking they are not the same thing (unless J = J0 = 0). here is the reference for J0: PHYSICAL REVIEW B 84, 115108 (2011). But I don't know how similar the results would be.

HTH

Matteo




Any suggestions would be very helpful.

Regards
Yuvam Bhateja
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Matteo Cococcioni
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University of Pavia
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