[QE-users] It is neccesary to make a vc-relax in each DFT U+V calculation?

[Timrov Iurii]

Dear Robert,

Originally, DFT+U and DFT+U+V were introduced to study transition-metal and rare-earth compounds. So usually, U has been applied to d and f electrons, and V for d-p and similar couples.

In your system, you have only s and p electrons. Now there are more and more studies where U and V are applied to these electronic states (see e.g. https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.2.043410). I do not have much experience in using DFT+U and DFT+U+V with U and V from linear response for these systems. But I know that ACBN0 is used quite extensively for these systems and U and V are positive.

HTH

Greetings,
Iurii


----------------------------------------------------------
Dr. Iurii TIMROV
Tenure-track scientist
Laboratory for Materials Simulations (LMS)
Paul Scherrer Institut (PSI)
CH-5232 Villigen, Switzerland
+41 56 310 62 14
https://www.psi.ch/en/lms/people/iurii-timrov
________________________________
From: ROBERT MIKHAIL GUZMAN ARELLANO <rguzmana at unmsm.edu.pe>
Sent: Saturday, September 28, 2024 02:03
To: Timrov Iurii <iurii.timrov at psi.ch>
Cc: users at lists.quantum-espresso.org <users at lists.quantum-espresso.org>
Subject: Re: [QE-users] It is neccesary to make a vc-relax in each DFT U+V calculation?

Thanks a lot for your response.

I was reading the paper that you recommended to me and I notice that your U and V values are positive.

I am practicing the DFT U + V in graphane (graphene -C- completely hydrogenated - 4 atoms in the unit cell) with the objective to calculate U and V values of carbon and hydrogen orbitals or between them. I used the protocol of your paper and I am considering the HSE band structure calculation as a target, where the last gives a greater gap energy than the GGA DFT calculations.

I obtained positive U values but the V values are negatives.

These are:

ATOMIC_SPECIES
 C  12.0107  C.pbe-n-kjpaw_psl.1.0.0.UPF
 H   1.008   H.pbe-kjpaw_psl.1.0.0.UPF
 ATOMIC_POSITIONS {angstrom}
C                0.0000000000        0.0489411798        4.0736189551
C                0.0000000000        1.5156118708        3.6147177498
H                0.0000000000        0.0493473355        5.1835009290
H                0.0000000000        1.5152618823        2.5048489230
 K_POINTS {automatic}
  12 12 1 0 0 0
HUBBARD ortho-atomic
V C-2P C-2P 1 1  2.8212
V C-2P C-2P 2 2  2.8212
V C-2P H-1S 1 3 -0.0283
V C-2P H-1S 2 4 -0.0283
V C-2P C-2P 1 2 -0.1355
V H-1S H-1S 3 3  4.3467
V H-1S H-1S 4 4  4.3467

So I am wondering what is the criteria to validate or accept a negative V, and another question is which orbitals need to be selected for a V and U calculations.  For example in the commented paper, the Mn-3d and O-2p orbitals are considered but avoided the others valence orbitals.  I am thinking that the most energetic orbitals of each atom must be considered... Could you recommend another work where discuss it ?

Thanks for the attention!!



El vie, 27 sept 2024 a las 3:01, Timrov Iurii (<iurii.timrov at psi.ch<mailto:iurii.timrov at psi.ch>>) escribió:
Dear Robert,

Please have a look at this paper: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.103.045141

Yes, generally, one should also redo the vc-relax calculations using updated U and V values using DFT+U+V. But if, for example, one wants to work with the fixed geometry (e.g. the experimental one), then obviously there is no need to do the vc-relax calculations.

Greetings,
Iurii

----------------------------------------------------------
Dr. Iurii TIMROV
Tenure-track scientist
Laboratory for Materials Simulations (LMS)
Paul Scherrer Institut (PSI)
CH-5232 Villigen, Switzerland
+41 56 310 62 14
https://www.psi.ch/en/lms/people/iurii-timrov
________________________________
From: users <users-bounces at lists.quantum-espresso.org<mailto:users-bounces at lists.quantum-espresso.org>> on behalf of ROBERT MIKHAIL GUZMAN ARELLANO via users <users at lists.quantum-espresso.org<mailto:users at lists.quantum-espresso.org>>
Sent: Thursday, September 26, 2024 17:34
To: users at lists.quantum-espresso.org<mailto:users at lists.quantum-espresso.org> <users at lists.quantum-espresso.org<mailto:users at lists.quantum-espresso.org>>
Subject: [QE-users] It is neccesary to make a vc-relax in each DFT U+V calculation?

Dear members,

I am starting to work in DFT U+V making calculations with pw.x and hp.x of Quantum Espresso package. So my question is:

In order to calculate the U and V values with hp.x. What is the path to follow?

At his time. I am doing these steps.

0. Calibrate pseudo potentials, k-points, and frequency of waves and density.

1. Calculate the crystalline structure using vc-relax.

2. Make a scf calculation using the best atomic positions and unit cell parameters obtained in vc-relax calculation. In this calculation, I put a small value of U and V between orbitals. (1.d-3 eV)

3 run hp.x in order to calculate better values of U and V.

4 extract the U and V values calculated by hp.x, and put these in a new scf calculation and run the last.

5 repeat the 3 step and after the 4 step until the U and V values between 2 different calculations look equal or with small difference (0.01eV).

My Question is: is it necessary to make a vc-relax between the 3 and 4 steps? I looked at some examples which do that  in order to calculate U value,but do not do the same when calculating V (interaction between different orbitals).

During this month I have been working with atoms whose valence orbitals are S and P, and I understand that for these orbitals, not being very localized like the D orbitals, it is necessary to work with U and V, where V responds to the coulomb interaction between orbitals of neighboring atoms.

Thank's for your attention.

Best regards.
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