[Pw_forum] convergence problem in scf calculation in rare earth oxide Sm2O3

[Thomas Brumme]

Dear Mohammed,

it's hard to give a general advice also because I didn't do many 
calculation with rare earth elements. Just checking the headers of the 
pseudos from the vlab side it seems both pseudos (LDA and GGA) have the 
same states in valence (l_max=3, number_of_wfc=number_of_proj=8). Did 
you try what they suggest on their side, i.e.:

"In some cases, defining orbital occupations (starting_ns_eigenvalue tag 
in Quantum ESPRESSO) is essential in order to converge calculations."

Maybe this can help to achieve convergence!? Otherwise, it might also 
help to ask them... Or try using the PAW pseudos from the pslibrary 
without the f-states, e.g., Sm.pbe-spdn-kjpaw_psl.1.0.0.UPF (or the 
ultrasoft one: Sm.pbe-spdn-rrkjus_psl.1.0.0.UPF).

And, of course, try what Karim and Ari said:
- increase ecutrho
- maybe ferromagnetic starting guess is wrong and you have to go for 
anti-ferromagnetic

Regards

Thomas


On 30.11.2017 11:43, Mohammed Khalafalla wrote:
> Dear Thomas,
> Thank you very much for your comments and suggestions.
> You are right the PBE pseudos from 
> http://www.vlab.msi.umn.edu/resources/repaw/index.shtml 
> <http://www.vlab.msi.umn.edu/resources/repaw/index.shtml> contains 
> f-states, but not the LDA ones (I noticed this simply by looking for 
> f-states within the pseudo files). So let me double check, shall I use 
> the LDA ones instead?
> Thanks ones more.
> Regards,
> Mohammed
>
>
> On 29 November 2017 at 11:24, Thomas Brumme 
> <thomas.brumme at uni-leipzig.de <mailto:thomas.brumme at uni-leipzig.de>> 
> wrote:
>
>     Dear Mohammed,
>
>     adding to the comments of Karim and Ari, I think that you should
>     consider using a pseudo without f-states - of course depending on
>     what you want to predict/calculate. In the end, you use DFT+U to
>     correct for the errors of DFT but putting the f-states into the
>     core is a first approximation to this idea. And the standard
>     ecutrho of 4 times ecutwfc is definitely not enough for PAW
>     potentials if the f shell is included.
>
>     Regards
>
>     Thomas
>
>
>     On 25.11.2017 20:16, Mohammed Khalafalla wrote:
>>     Dear all,
>>     I could not achieve scf convergence in Sm2La2O6 (the input file
>>     is attached herewith). This was the case even after several
>>     'restart' of the calculation with different pseudpotentials
>>     specially for 'O' atom. I guess I used well tested PAW psedu for
>>     rare earth from
>>     http://www.vlab.msi.umn.edu/resources/repaw/index.shtml
>>     <http://www.vlab.msi.umn.edu/resources/repaw/index.shtml>
>>     I used recommended hubbard potentials and spin polarization, but
>>     no change. Generally I found convergence in (Sm,O) system to be
>>     difficult. Can you kindly let me know which parameter set-up
>>     would determine successful convergence in (Sm,O) system?
>>     Regards,
>>     Mohammed A. H. Khalafalla (PhD)
>>     Taibah University
>>     KSA
>>
>>
>>
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>
>     -- 
>     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 <mailto:thomas.brumme at uni-leipzig.de>
>
>

-- 
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

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