[QE-users] [SPAM] Re: Re: Assistance with Convergence Issues of Surface Calculations

[Giuseppe Mattioli]

Dear Vinay Maithani
Ok, let us say "unconventional amorphous structure" as you are sure  
that it is meaningful, for the sake of discussion, even if I don't see  
any pattern or repeated unit in the structure and I see strange P-S  
"molecules" and direct Al-Li and Li-Li bonds which are unconventional.  
Only for my curiosity, can you post a link to some publication where  
this or a similar structure is investigated?

However, the structure is so unconventional that it is possible that  
you aren't able to obtain convergence, no matter what you try. To give  
it a try I suggest that you:

1) start it simpler (no dipole correction, gamma point as the  
structure doesn't seem periodic).

2) If you are using NC pseudopotentials (which ones?), then raise  
ecutwfc as there are no Li pp in my experience that is well converged  
at 50 Ry. You don't need to indicate ecutrho, instead, when you use NC  
PPs.

3) Don't specify nbnd when using occupation='smearing', the code  
provised all the orbitals you need. Try Gaussian smearing, first, as  
it is more stable.

4) Try to reduce electron_maxstep to a much smaller value (if it  
doesn't converge after 50-100 step it will probably not converge after  
2000), and use this smaller value together with  
scf_must_converge=.false. This will force the bfgs step on an  
unconverged wavefunction, and can be very helpful to move your system  
out of an unlucky initial structure with a few BFGS steps. However,  
your structure is so unconventional that even such trick may fail.

HTH
Giuseppe


Quoting Vinay Maithani <vinaymaithani21 at kgpian.iitkgp.ac.in>:

> Dear Giuseppe,
>
> Thank you for your feedback. I would like to clarify that this is an
> *asymmetric
> polar slab* structure of a *solid-state electrolyte*. I have thoroughly
> checked the structure, and it appears correct based on my verification.
>
> Could you please explain why you believe the slab is wrong? Your insights
> would be helpful as I continue to address the convergence issue.
>
> On Wed, Sep 4, 2024 at 3:26 PM Vinay Maithani <
> vinaymaithani21 at kgpian.iitkgp.ac.in> wrote:
>
>> Dear Quantum ESPRESSO community,
>>
>> I hope this email finds you well.
>>
>> I am currently working on large band gap semiconductors and have
>> encountered persistent difficulties in achieving convergence while
>> calculating the surface properties of these materials. Below are the
>> strategies I have attempted so far:
>>
>>    - *Mixing Beta:* Adjusted up to 0.1
>>    - *Mixdim:* Increased to 24
>>    - *Smearing:* Gaussian with degauss = 0.2
>>    - *Nbnd:* Added a minimum of 20% more than the number of Kohn-Sham
>>    states
>>    - *Ecutwfc:* Increased from 50 Ry to 70 Ry
>>    - *Ecutrho:* Set to 8 times Ecutwfc
>>    - *Electron Max Step:* Extended to 2000 steps
>>
>> Despite these efforts, my calculations still fail to converge, returning
>> the error:
>> *“Convergence NOT achieved after *** iterations: stopping.”*
>>
>> I am using norm-conserving pseudopotentials and have applied dipole
>> corrections, but the issue persists. I have attached the input and output
>> files, along with the plot of potential data obtained via pp.x
>> (plot_num=11) and averaged in the xy-plane where a discontinuity occurs in
>> the vacuum region, available here: Google Drive link
>> <https://drive.google.com/drive/folders/1HoSFk11TMN4qAo8jZoSvyEymK92xGu2r?usp=drive_link>
>> .
>>
>> I would greatly appreciate any insights or suggestions you may have to
>> help resolve this problem.
>>
>> Thank you for your time and guidance.
>>
>> Best regards,
>> Vinay Maithani
>> PhD Candidate, IIT Kharagpur
>> vinaymaithani21 at kgpian.iitkgp.ac.in
>>



GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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E-mail: <giuseppe.mattioli at ism.cnr.it>