[QE-users] Regarding "occupations" keyword in input file

[Timrov Iurii]

Dear Yuvam Bhateja,


> I am also simulating the same AFM Mott insulator.

> For structural optimization I usually use occupation="smearing" and smearing="Gaussian".
> Is it the correct way or should I choose different options.


That is fine. You can use also other smearing options, but in any case since your system has a gap and you use the smearing then your system is considered as a fake metal. So the type of smearing does not really matter for magnetic insulators. For magnetic insulators, smearing is needed only for technical reasons: in order to use starting_magnetization, the PW code requires smearing. But once the calculation is converged, you can perform a second SCF calculation with fixed occupations and by setting total magnetization and starting from the previous converged SCF calculation (reading wavefunctions and density/potential). After this second SCF, you will have a magnetic insulator with no smearing. After this you can perform various linear response calculations (PH, HP, etc.).


But for DOS you do not need to play this trick with two SCF calculations. One SCF (the first one) is already enough. Then you can compute DOS using the tetrahedron method or with the smearing if you want.


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: Friday, August 14, 2020 9:41:58 PM
To: Quantum ESPRESSO users Forum
Subject: Re: [QE-users] Regarding "occupations" keyword in input file

Hello,

I had the same question actually.
I am also simulating the same AFM Mott insulator.
For structural optimization I usually use occupation="smearing" and smearing="Gaussian".
Is it the correct way or should I choose different options.

And during DOS I use occupation="tetrahedra" with the relaxed calculation.

Please guide me with this problem.

Regards
Yuvam Bhateja
IIEST Shibpur
India

On Fri, 14 Aug 2020, 3:49 pm Matteo Cococcioni, <matteo.cococcioni at unipv.it<mailto:matteo.cococcioni at unipv.it>> wrote:
In addition to what Iurii says, if you use occupation="smearing" the phonon code will assume your system is metallic and will never compute the dielectric tensor and Born effective charge which you need, instead to get the LO-TO splittings at Gamma (non analytic part of the dynamical matrix).

Greetings,

Matteo


Il giorno gio 13 ago 2020 alle ore 20:11 Timrov Iurii <iurii.timrov at epfl.ch<mailto:iurii.timrov at epfl.ch>> ha scritto:

Dear Mohaddeseh,


To perform linear response calculations (phonons, calculation of Hubbard parameters, etc.) for magnetic insulators, I use the procedure described in q-e/HP/examples/example02/README.


If you have a gapped system, you should not use smearing, because there can be numerical issues (due to the division by zero, because the DOS at the Fermi level can be very small using small smearing for insulators, see Eq. (79) in Rev. Mod. Phys. 73,  515 (2001)).


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<mailto:users-bounces at lists.quantum-espresso.org>> on behalf of Mohad Abbasnejad <mohaddeseh.abbasnejad at gmail.com<mailto:mohaddeseh.abbasnejad at gmail.com>>
Sent: Thursday, August 13, 2020 7:58:21 PM
To: users at lists.quantum-espresso.org<mailto:users at lists.quantum-espresso.org>
Subject: [QE-users] Regarding "occupations" keyword in input file

Dear QE users,

Hello

I have a general question.
My structure is Mott hubbard and has a band gap of about 2 eV. It is also antiferromagnetic in its ground state.
I can obtain antiferromagnetic state and the desired band gap with hubbard parameters by both ways:
occupations: smearing
occupations: fixed
A) I am wondering whether these occupations can have effect on the phonon frequencies?
B) When is it preferable to use occupation fixed in our calculations?

Any help would be appreciated.
Thanks in advance.

Regards,
Mohaddeseh

--
---------------------------------------------------------
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>
---------------------------------------------------------

_______________________________________________
Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso<http://www.max-centre.eu/quantum-espresso>)
users mailing list users at lists.quantum-espresso.org<mailto:users at lists.quantum-espresso.org>
https://lists.quantum-espresso.org/mailman/listinfo/users


--
Matteo Cococcioni
Department of Physics
University of Pavia
Via Bassi 6, I-27100 Pavia, Italy
tel +39-0382-987485
e-mail matteo.cococcioni at unipv.it<mailto:lucio.andreani at unipv.it>
_______________________________________________
Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso<http://www.max-centre.eu/quantum-espresso>)
users mailing list users at lists.quantum-espresso.org<mailto: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/20200817/58bada57/attachment.html>