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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