[Pw_forum] testing HSE for BCC Fe

[Daniel Stoeffler]

Hello Paolo, 

Thank you for your answer. 

Up to now, I used the
FLEUR, Abinit and the VASP codes and I am doing some tests to see if it
would be interesting (or not) for my studies to use also QE. 

I found
the computation "surprisingly" huge because when I compare to the VASP
code with the same parameters (Ecutoff, NKpoints, Nq) and with the HSE06
functional, after onr night of run, I got a few tens of iterations
whereas I got only one with QE :(. 

For these tests, I compare 2
pseudopotential-based methods for the same parameters which I can
control via the input file (Ecutoff and Kpoints). I have compared the
(defaut) q-points and they are identical for the VASP and the QE codes.


I will try the "tqr=.true." option and let you know. 

Concerning the
Pseudopotential, I decided to use Fe.pbe-sp-van.UPF in order to keep the
Ecutoff small : I tried HGH but the Ecutoff needed for magnetic systems
is very large and I have avoided to use NLCC pseudopotentials which are
not compatible with hybrid functional (is this correct ?). 

The final
system I would investigate is the Fe(FeCo)O4 spinel with a 28-atoms into
cell using hybrid functionals : from your experience and knowlege, it
this hopeless with QE or not ? 

Best wishes, 

Daniel 

Le 2016-09-09
10:21, Paolo Giannozzi a écrit : 

>> The computational complexity of a
calculation with hybrid functionals goes as (Nk*Nb)^2*Npw log(Npw) or
so, where Nk=number of k-points, Nb=number of occupied bands, Npw=number
of plane waves; with GGA functionals, as Nk*Nb*Npw log(Npw) or
Nk*Nb*Npw^2
> 
> well, no, as Nk*Nb*Npw log(Npw) or Nk*Nb^2*Npw
> 
>
Paolo
> 
>>> could you try to explain me how to reduce the computation
time
>> 
>> first of all you may try to reduce one of the sums over
k-points using options nq1,nq2,nq3, as explained in the example for
hybrid. For a metal, not sure it works well, though. Since you are using
UltraSoft PseudoPotentials, try option "tqr=.true." (real-space
treatment of augmentation functions): it should give a significant
speedup. Another significant improvement is contained in the forthcoming
6.0 version of QE, but it doesn't work yet for USPP
>> 
>> Paolo -- 
>>

>> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
>>
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
>> Phone
+39-0432-558216 [1], fax +39-0432-558222 [2]
> 
> -- 
> 
> Paolo
Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> Univ.
Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone
+39-0432-558216, fax +39-0432-558222
> 
>
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> Pw_forum mailing
list
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> http://pwscf.org/mailman/listinfo/pw_forum
[3]
 

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------
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[2]
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