[QE-users] Structural stability problem

[Nicola Marzari]

Dear Wei Gui,


you could also test your PWscf input file in
https://www.materialscloud.org/work/tools/qeinputgenerator

This would take your current structure, and generate a new input
for PW with parameters and pseudopotentials we think are optimal. Would
be interesting to see if it helps.

			nicola


On 12/09/2019 09:50, Pietro Davide Delugas wrote:
> Hello
> What value are you using for conv_thr in the electrons namelist ? You 
> should use a value which is rather lower than the default at least 
> something like 1.d-9. It this is the case the should be some warning 
> just after the forces summary at the end of each force computation.
> I hope this helps
> Pietro
> 
> 
> On 9/12/19 3:33 AM, Gui Wei wrote:
>> Dear QE users,
>>
>> When I optimized the structure of a heterostructure (containing about 
>> 130 atoms),it does converges as expected,and there is basically no 
>> problem with the atomic structure.The convergence threshold I used was 
>> *etot conv thr: 2.0D-4* *forc_conv_thr:2.0D-3*.By comparing with the 
>> parameter design in the literature (similar model，usually using 
>> software VASP),I think this convergence accuracy is relatively 
>> rough,especially force.So I raised the threshold to *etot conv thr: 
>> 1.0D-4 * *forc_conv_thr:2.0D-3.*At this point I found that the 
>> structure optimization could not converge.I extracted the data from 
>> the output document and plotted Energy difference-Scf cycles curve and 
>> Max force-Scf cycles curve.I found that scf cycles =5 satisfies the 
>> convergence of the former rough convergence(both energy and 
>> force).After that,two curves rise synchronously,this means that the 
>> latter's fine convergence accuracy will never be achieved.
>> What I want to know is whether the atomic structure under the rough 
>> precision can be counted as a stable structure.If so, how do I 
>> understand the rise of the above two curves (this seems to be that the 
>> structure is not stable, in my understanding, if it is a stable 
>> structure, the two curves should continue to slowly decline, 
>> eventually reaching an almost horizontal state).If not, what is the 
>> solution?
>>
>> Wei gui
>> School of Mechanical Engineering，Chongqing University, China
>>
>>
>>
>>
>>
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> 
> 
> 
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-- 
----------------------------------------------------------------------
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
Director, National Centre for Competence in Research NCCR MARVEL, EPFL
http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project