[QE-users] QE-input file clarification

[Nicola Marzari]

Thank you Giovanni!

And as a reminder to everyone, there is the Quantum ESPRESSO input 
generator on the Materials Cloud that can offer some sanity checks - you 
upload a structure, and it tells you a reasonable set of input 
parameters and pseudopotential suggestions:

https://qeinputgenerator.materialscloud.io

			nicola




On 30/09/2025 10:03, Giovanni Cantele wrote:
> Hi,
> 
> first of all, I suggest checking your input structure. The input files 
> you attached are in html format, so
> it is difficult for me to try to open the file using programs able to 
> visualize the structure. This is the first task to
> be done before running any calculation.
> 
> Second, you said you did several trials, but you did not say which! So, 
> it is difficult to suggest what to change
> if we do not know what you did.
> 
> Third, there is no output file, which also might be helpful in trying to 
> figure out what's happening. For example: did you plot
> the bands "as are" or you shifted by the proper Fermi energy? Are you 
> sure that you are not seeing the wrong energy interval?
> 
> Fourth, after a quick inspection of your inputs (that in html format are 
> a mess!) , it seems to me that a 120 Ry ecutwfc is too high for a PAW 
> pseudopotential.
> If you reduce it, then reduce ecutrho accordingly.
> 
> As far as the question about the basis set is concerned, it is a long 
> standing problem. With localized basis sets you reduce significantly the 
> computational cost
> of the calculation, but you should be aware of numerical problems 
> related to basis set size, non orthogonality of orbitals, systems where 
> you need basis set functions
> located not at atomic positions, and so on. A plane-wave basis set is 
> numerically more expensive, but allows you to control the convergence 
> with respect to the
> basis set using a single parameter, the cutoff (ecutwfc in QE). Being a 
> basis set of functions which are delocalized, a side effect is that they 
> are non zero also in the vacuum regions
> where you expect nearly zero charge density. However, this turns out to 
> be also an advantage, because it means that the basis set has no 
> "spatial dependence", that is, given the unit cell and
> the cutoff(s), it is independent on the atomic species and/or positions 
> you put therein.
> 
> 
> If you provide more details, we could try to understand whether or not 
> your calculation is wrong.
> Giovanni
> -- 
> 
> Prof. Giovanni Cantele
> Dipartimento di Fisica "Ettore Pancini"
> Universita' degli Studi di Napoli "Federico II"
> Complesso Universitario M. S. Angelo - Ed. 6
> Via Cintia, I-80126, Napoli, Italy
> e-mail: giovanni.cantele at unina
> Phone: +39 081 676910
> 
> Web page: https://sites.google.com/view/giovanni-cantele/home <https:// 
> sites.google.com/view/giovanni-cantele/home>
> 
> 
> Il giorno mar 30 set 2025 alle ore 09:23 Jodan Ebaya 
> <jpebaya at carsu.edu.ph <mailto:jpebaya at carsu.edu.ph>> ha scritto:
> 
>     Good day!
> 
>     I am Jordan Lee Ebaya, a second MS-PHYSICS students of Mindanao
>     State University Iligan Institute of Technology, Iligan CIty,
>     Philippines. Currenlty i am working with my graduate research which
>     Focus on DFT calculation using Qunatum Espresso.
> 
>     I just want to ask if my input files in QE is wrong since i already
>     have done several trials and still i did not get the result i
>     wanted. Base on the journal Iread that was publish on RSC, thier
>     calcualtion shows that there is a 0.3eV bandgap of the Magnesium
>     Dicarbide using Amsterdam Desnity Functional Simulation Package ADF-
>     BANDS with Slater Type Orbital, Double Zeta Polarized Basis set. I
>     also want to know, what are the cons and pros of using differenet
>     basis sets?
> 
>     Attached documents are my relax, scf, nscf(bands) input file and the
>     resulted bands strutre.
> 
>     Thank you and hoping for an answer for this inquery, this will be a
>     great help for my thesis.
> 
>     Sincerely,
> 
>     Jordan Lee P. Ebaya
>     /MS-PHYSICS Students/
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-- 
----------------------------------------------------------------------
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
Director, National Centre for Competence in Research NCCR MARVEL, SNSF
Laboratory Head, PSI Center for Scientific Computing, Theory, and Data
Contact info and websites:  https://theos-wiki.epfl.ch/en/Main/Contact