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

Mon Aug 17 11:31:20 CEST 2020

Dear Dr. Lurii,

Thank you so much for this great advice.

Regards
Yuvam Bhateja

On Mon, 17 Aug 2020, 2:09 pm Timrov Iurii, <iurii.timrov at epfl.ch> wrote:

> 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> 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> 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> on behalf of
>>> Mohad Abbasnejad <mohaddeseh.abbasnejad at gmail.com>
>>> *Sent:* Thursday, August 13, 2020 7:58:21 PM
>>> *To:* 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
>>> Website:  academicstaff.uk.ac.ir/moabbasnejad
>>> ---------------------------------------------------------
>>>
>>> _______________________________________________
>>> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso
>>> )
>>> users mailing list 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 <lucio.andreani at unipv.it>
>> _______________________________________________
>> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
>> users mailing list users at lists.quantum-espresso.org
>> https://lists.quantum-espresso.org/mailman/listinfo/users
>
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