[Pw_forum] hybrid functional

"Valentina Dellacà C.R.F. S.C.p.A." valentina.dellaca at tirocinanti.crf.it
Wed Apr 10 09:07:28 CEST 2013


Dear  Monhish,
thanks again for your answer. So, if I am understanding correctly I 
should just perform a scf run with a dense k-point grid and then go on 
with the DOS using projwfc.x or dos.x, that's right? I was performing a 
nscf run after the scf one because I was following the tutorial:

http://www.fisica.uniud.it/~giannozz/QE-Tutorial/
*Post-processing and data analysis* (slides 
<http://www.fisica.uniud.it/%7Egiannozz/QE-Tutorial/tutorial_postproc.pdf>, 
examples 
<http://www.fisica.uniud.it/%7Egiannozz/QE-Tutorial/examples_postproc.tgz>)

Regards,
Valentina


Il 04/09/2013 04:20 PM, mohnish pandey ha scritto:**
> Dear Valentina,
>
> You can do the calculations with the SCF run in HSE/PBE0, that 
> shouldn't be a problem. And why do you need nscf calculation anyway to 
> do the DOS calculation. 'nscf' calculation is needed when you are 
> interested in band-structure where you use the ground state charge 
> density for interpolation along certain directions. Your scf 
> calculations will won't have any problem in calculation the DOS. Hope 
> it helps :)
>
>
> On Tue, Apr 9, 2013 at 3:10 PM, "Valentina Dellacà C.R.F. S.C.p.A." 
> <valentina.dellaca at tirocinanti.crf.it 
> <mailto:valentina.dellaca at tirocinanti.crf.it>> wrote:
>
>     Dear Arles,
>     thanks for your answer. My doubts are about the employment of the
>     projwfc.x, post processing tool, when using hybrid functional, 
>     since the README of the hybrid functional tutorial says that one
>     gets into troubles when performing non-scf calculations. At the
>     moment I see the way to proceed if I wish to plot the band
>     structure from the log file of the scf run, but i do not know how
>     to get informations about the dos from such file, since it (as far
>     as I understand) seems to be the only run i can perform when
>     employing hybrid functionals. Do you know how to get informations
>     about the dos from the .log of a scf run?
>     Thank you!!!
>     Valentina
>
>     Il 04/09/2013 02:24 PM, Arles V. Gil Rebaza ha scritto:
>>     Dear Valentina,
>>     Yes, projwfc.x is a postprocessing tool like dos.x, whether you
>>     want to get only the density of state, "dos.x" is enough, whereas
>>     "projwfc.x" you can obtain DOS, projected DOS (PDOS) and the
>>     magnetic moment per atom too.
>>     http://www.quantum-espresso.org/?page_id=876
>>
>>     Best
>>
>>     PhD Arles V. Gil Rebaza
>>     Instituto de Física de La Plata
>>     Argentina
>>
>>
>>     2013/4/9 "Valentina Dellacà C.R.F. S.C.p.A."
>>     <valentina.dellaca at tirocinanti.crf.it
>>     <mailto:valentina.dellaca at tirocinanti.crf.it>>
>>
>>         Dear Mohnish,
>>         thanks for you answer. I will follow your suggestion and try
>>         also HSE, with a coarser k-point mesh, (indeed with PBE0 the
>>         computation time is quiet large), and I did not know about
>>         projwfc.x.
>>         I have a further question concerning the DOS. If I wish to
>>         know about the DOS of my system, which uses  the hybrid
>>         functional implementation, am I able to use the projwfc.x?
>>         Is'n it a postprocessing tool?
>>         Thanks,
>>         regards,
>>         Valentina
>>
>>         Il 04/09/2013 11:18 AM, mohnish pandey ha scritto:
>>>         Hi,
>>>
>>>         As far as I can understand there is no rule. It depends how
>>>         fine you want to represent your Fock operator. Normally
>>>         calculations of the Fock exchange in expensive, so its not
>>>         affordable to do very fine grid calculations  So I suggest
>>>         you start with low nqx(1, 2, 3) and increase it
>>>         systematically. Increasing it will give you better results(
>>>         I mean converged results, not necessarily close to
>>>         experiments).
>>>
>>>         Just an advice, PBE0 needs much more high density k-point
>>>         mesh for the convergence of Fock exchange since it's a long
>>>         range interaction. So you have to do calculations with high
>>>         density of k-points. But if you use HSE instead of PBE0 you
>>>         get away with coarser k-point mesh since it involves
>>>         screened exchange interaction which converges much faster
>>>         than bare Coulomb exchange as in PBE0. Regarding to the DOS
>>>         plot you will find a nice tutorial on Heither's website, I
>>>         am pasting the link
>>>         http://www.stanford.edu/~hkulik/www/Tutorials/Entries/2012/1/24_Population_analysis_and_PDOS.html
>>>         <http://www.stanford.edu/%7Ehkulik/www/Tutorials/Entries/2012/1/24_Population_analysis_and_PDOS.html>
>>>
>>>
>>>         On Tue, Apr 9, 2013 at 10:05 AM, "Valentina Dellacà C.R.F.
>>>         S.C.p.A." <valentina.dellaca at tirocinanti.crf.it
>>>         <mailto:valentina.dellaca at tirocinanti.crf.it>> wrote:
>>>
>>>             Hi,
>>>             I am a Quantum Espresso beginner user, and I am
>>>             simulating the Ta2O5 structure, with the employment of
>>>             the hybrid functional PBE0. I have some questions :
>>>
>>>             - if I choose a k-point grid not in automatic, how
>>>             should I pick the nqx1,2,3? Is there a rule?
>>>             - when one wishes to have informations (ex. plot) about
>>>             the density of states from the scf run, how should I
>>>             proceed?
>>>
>>>             Thank you,
>>>             regards
>>>             Valentina
>>>>
>>>>             -- 
>>>
>>>
>>>             -- 
>>>
>>>             _______________________________________________
>>>             Pw_forum mailing list
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>>>
>>>
>>>
>>>
>>>         -- 
>>>         Regards,
>>>         MOHNISH,
>>>         -----------------------------------------------------------------
>>>         Mohnish Pandey,
>>>         PhD Student,
>>>         Center for Atomic Scale Materials Design,
>>>         Department of Physics,
>>>         Technical University of Denmark
>>>         -----------------------------------------------------------------
>>
>>
>>         -- 
>>
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>>
>>
>>
>>     -- 
>>     ###--------->   Arles V. <---------###
>
>
>     -- 
>
>     _______________________________________________
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>
>
>
> -- 
> Regards,
> MOHNISH,
> -----------------------------------------------------------------
> Mohnish Pandey,
> PhD Student,
> Center for Atomic Scale Materials Design,
> Department of Physics,
> Technical University of Denmark
> -----------------------------------------------------------------


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