[QE-users] Calculation of epsilon.x

[Pietro Delugas]

Dear Anuja

the calculation with a very dense k-point mesh is most likely looping 
through the k points and taking a lot of time before printing out anything.

It is not necessary though to run the scf calculation with the very fine 
mesh; it is sufficient to run the scf calculation with a feaisble k 
point mesh for which you are confident to be at convergens, once done 
the scf calculation with the feasible converged mesh  you may run  nscf 
calculation with the finer mesh that you  need for the epsilon.x 
calculation.

To speed up the calculation you may try to use the k-point parallelism: 
in suppose that you are using 20 MPI processes and that 4 of them are 
sufficient to run the iterative diagonalization for one k point, you can 
divide your 20 MPI processes in 5 pools each diagonalizing and assigned 
subset of the total k points. To do this you just have to run your pw.x 
command as:

mpirun -np 20 pw.x -nk 5 -i input_nscf > out_nscf

I hope this helps.

kind regards - Pietro

On 01/07/19 17:44, Anuja Chanana wrote::
> Dear all,
> I am trying to run epsilon.x by reading the following tutorial
> https://www.paradim.org/sites/default/files/2019-05/Band_Structure_and_UV-VIS_Spectra.pdf 
>
>
> The manual says that for the calculation of epsilon, a finer-k mesh is 
> required like 30x30x30.
> I have a triclinic system where
> a = 6.3 A  b = 6.5 A  c = 5.9 A
> alpha 121.358  beta 88.3349  gamma 106.391
>
> If I increase the k-mesh to 30x30x30, the initial scf simulation 
> doesn't run at all.
> Nothing gets written. Why does that happen?
> Has anyone experienced it before?
>
> Thanks
> Anuja
>
>
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