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

[ROBERT MIKHAIL GUZMAN ARELLANO]

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 -0.0283V C-2P H-1S 2 4 -0.0283V 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>)
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> on behalf of
> ROBERT MIKHAIL GUZMAN ARELLANO via users <users at lists.quantum-espresso.org
> >
> *Sent:* Thursday, September 26, 2024 17:34
> *To:* users at lists.quantum-espresso.org <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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