[Pw_forum] Problems with phonones in Fe

Иван Булдашев buldashev.ivan at mail.ru
Mon Oct 28 10:24:22 CET 2013

Dear users, thanks for your replies, but I had some questions yet.
Firstly, with one Fe atom in BCC cell and 4x4x4 k-point grid my task 
works faster, but it took two days. Are there any reasons for so long 

 >> For iron on 48 cores I would probably parallelize on k-points using 
npools, if the memory allows.

I do not use it. If I understand right, the key "-npool" can accelerate 
calculation, because it divide process?

 >> You are using a 8x8x8 grid in the cubic cell, do you really need it 
for thermodynamic quantities?

My calculation was based on paper Tilmann Hickel and Joerg Neugebauer, 
they used PHON (small displacement method) and took big grid. And I 
can't find the same work with QE using. Can I get high accuracy with 
4x4x4 grid?

 >> As you see, even if it costs a bit more, I use a more strict 
convergence threshold. Try to decrease your value.

I try 1e-16 and it works very long. Can I get same accuracy with 
threshold = 1e-12?

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