[QE-users] seeking hints for nscf convergence in supercell

[patrizio.graziosi at cnr.it]

Hello everybody,

I'm seeking advice to fasten nscf convergence (or make it possible).

I'm using qe 6.8 to study Mg3Sb2 / Mg3Bi2 solid solutions, as first  
step I'm starting with a Mg3Sb2 2x2x2 supercell (40 atoms) to compare  
with simple Mg3Sb2 cell (5 atoms).

The calculation track is scf --> nscf --> fs.

For the simple cell it runs smoothly (and I'm confident it is okay as  
I compared with a colleague of mine relatively expert in DFT, not qe).

For the supercell the scf converges in around 1 day of CPU time, but  
the nscf does not converge in ~ 12 days of CPU time - say 23 hours  
with 4 nodes, 6 tasks, 6 cpu-per-task, npool=24, are not sufficient to  
reach convergence.

I attach the .in files for both scf and nscf, as well as the nscf out  
file. There are several eigenvalues not converged but I am not sure if  
this is the cause of the long time required for convergence (I've read  
in the forum this can be often regarded as a warning).

So, since I have limited computational resources, before making many  
trial-and-error attempts I would seek hints and advices to understand  
if it is only a matter of make a more intensive calculation (I've read  
the restart mode is not recommended for nscf so I should ask for more  
nodes), or to improve the input file in an aware way.


Sorry if this is a time waste for you, and thanks in advance for any support,

Patrizio

-- 

Patrizio Graziosi, PhD

Research Scientist

CNR - ISMN
Institute for the Study of Nanostructured Materials
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