[QE-users] DFT Calculation with expermental results

[Yuvam Bhateja]

Hey,

I am no expert either but I will try to help with what I have learned so
far.

1) Yeah, you can initiate the calculation with your original cell parameter
and then go relaxing your cell and atoms. And then that final cell
parameter can be used for single point calculation (scf) to find band gap
which you can compare with your experimental data.

2) Cell parameter are also important and needed to relax. You can use
cell_dofree="ibrav" in CELL card (check input file of pw.x). In this way
your cell parameters will be relaxed keeping the lattice shape constant.

3) Choice of pseudopotential majorly depends on your XC functional. From
what I have learned and observed, PBEsol is a good choice if one is
focusing on lattice parameters and structure of cell. PBE is good for
properties like bandgap, spin, etc. revPBE is good if you are dealing with
Van Der Waal interactions, etc. You need to choose what you want to focus
on and can refers to papers to check what suits you best.

4) So, in single point calculation output, at the end you can see that
there will be two terms, total magnetization and absolute magnetisation. If
there is zero value for total and non zero value for absolute it means
there is magnetisation per atom but cancelling out each other to make it
zero i.e., Antiferromagnetic. If both the values are non zero and same then
all magnetic moments are aligned i.e. Ferromagnetic.

5) You can adjust your total magnetization using tot_magnetization. If you
keep it 0, the calculation will be performed under this constraint and you
might get an AFM. Similarly for FM, assign a value you find suitable. Then
you can compare the energies from two different outputs.

Also, since you are dealing with Transition metals, make sure you use
DFT+U.
You can either calculate the U parameter or can use that are available in
already published works.

Please let me know if you have any more doubts.

Regards
Yuvam Bhateja
B.Tech.
IIET Shibpur
India


On Mon, 28 Sep 2020, 2:40 am Ismail BENAICHA, <benaicha.ismail at uit.ac.ma>
wrote:

> dear Users, hope you are doing well.
> my name is Ismail a Ph.D. Moroccan student.
> Please I have some questions if you don't mind.
> I am trying to study the magnetic behaviour of thin layers of ZnO doped
> with transition metals (Co, Ni, Fe) using DFT calculation, I am a beginner
> on DFT calculation using quantum espresso, my questions are:
> 1-Sir/madam, if I want to combine an experimental result (E_gap from
> UV-visble analysis and cell parameter from XRD analysis) with the DFT
> calculation and compare them. Should I change the cell parameters of my
> super cell in the inpult file with the ones from XRD analysis then run my
> calculation (RELAX, SCF, BAND, DOS), or should I run my calculation
> normally then compare the results that I get?
>
> 2- Sir/madam, If i want relax my super cell without losing my Ibrav
> structure should I choose "vc-relax" or "relax" in ''calculation="
>
> 3-Sir/madam, how do you choose the pseudopotential that you will be
> working with and  how do I choose the pseudopotential if I want to perform
> a DFT calculation using GGA ?
>
> 4-Sir/madam, how I can decide that I have FM, AFM at the end of the
> calculation, if I perform a spin-polarized calculation?
>
> 5- Sir/madam, where can I find energy difference DeltaE=E(AFM)-E(FM) in
> the output of SCF file?
>
>
> thank you in advance
> --
> *Benaicha Ismail *
> Ph.D student. Calculation and Modeling of Physical Properties of Solid
> Materials at (LPMC-UIT. FS. Kénitra)
> Email-1- :benaicha.ismail at uit.ac.ma
> *Email-2-* :ismail.benaicha at gmail.com
>
>
> <https://www.facebook.com/profile.php?id=100011444409108>
> <https://www.linkedin.com/in/ismail-benaicha-367782105/> .
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20200928/4dacbd20/attachment.html>