[QE-users] Convergence in Hexagonal Systems

[Dr. Thomas Brumme]

Dear Dr. Anuja Chanana,

without more information, we (everyone here in this users list) can't  
help you.
What do you mean with "difficult to reach on convergence"? How do you  
test convergence?

Is an scf cycle not converging? Assuming you calculate a "meaningful"  
structure, this
could either mean you need to increase the wave-function or the  
charge-density cutoff
or both. Or the k-point sampling. Again, I don't think it is a problem  
of the pseudo.
For both N and B, creating pseudos is pretty straightforward and I  
don't think the
pseudos of the PSlibrary are wrong or bad. On the other hand, looking  
at this site:

https://www.materialscloud.org/discover/sssp/plot/efficiency/N

I see that for a nitrogen PBE US pseudo of the PSLibrary a cutoff of  
40 Ry might be
just too small, especially when you want to relax the cell. For  
accurate forces and
pressure you always need a higher cutoff. (PBE is nearly PW91 but for  
the latter, I
guess, you need a higher cutoff)

What do you mean with "its difficult to reach on convergence"?  
Furthermore, why do
you use a smearing if the system is an insulator?

Regards

Thomas

P.S.: Please, always reply to "All", i.e., also to the list, so that  
others can
find the answer if they have the same problem.

Zitat von Anuja Chanana <anujachanana26 at gmail.com>:

> Dear Dr. Thomas Brumme,
> Thanks for the information.
> I tested the pseudopotential for bulk BN hexagonal system as well. But its
> difficult to reach on convergence.
> PFA the input file.
>
>
> Thanks and Regards
> Dr. Anuja Chanana
>
>
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> 02/09/19,
> 11:08:44 PM
>
> On Sat, Feb 9, 2019 at 10:19 PM Dr. Thomas Brumme <
> thomas.brumme at uni-leipzig.de> wrote:
>
>> Dear Anuja Chanana,
>>
>> I don't think it is the pseudo which gives problems in one case and none
>> in the other. Looking at the structure I guess that you want to
>> simulate an isolated
>> layer in the hexagonal system, don't you? Otherwise it would make no
>> sense to have a vacuum of 6 Angstrom. But then, why do you have only
>> 6 Angstrom? And why do you use k-point sampling in a non-periodic
>> direction?
>> Furthermore, your in-plane k-point sampling is different in both systems
>> which
>> could explain other differences!? If you really want to simulate a 2D
>> system have a look at the input variable
>>
>> assume_isolated='2D'
>>
>> Otherwise, if you don't want to simulate a 2D system, please check your
>> structures with, e.g., XCrysDen.
>>
>> Regards
>>
>> Thomas Brumme
>>
>>
>> Zitat von Anuja Chanana <anujachanana26 at gmail.com>:
>>
>> > Hello all,
>> > I am trying to converge a hexagonal and cubic system of BN. The cubic
>> > system shows a convergence while the hexagonal system doesn't, though the
>> > parameters are the same. I guess there might be some issue in the
>> Nitrogen
>> > pseudopotential. Can you please look into the issue?
>> > PFA the input files for both the systems.
>> >
>> >
>> >
>> > Thanks and Regards
>> > Dr. Anuja Chanana
>> >
>> >
>> >
>> > [image: Mailtrack]
>> > <
>> https://mailtrack.io?utm_source=gmail&utm_medium=signature&utm_campaign=signaturevirality5&
>> >
>> > Sender
>> > notified by
>> > Mailtrack
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>> > 02/09/19,
>> > 2:41:41 PM
>>
>> --
>> Dr. rer. nat. Thomas Brumme
>> Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry
>> Leipzig University
>> Phillipp-Rosenthal-Strasse 31
>> 04103 Leipzig
>>
>> Tel:  +49 (0)341 97 36456
>>
>> email: thomas.brumme at uni-leipzig.de
>>
>>