[Pw_forum] testing HSE for BCC Fe
daniel.stoeffler at ipcms.unistra.fr
Fri Sep 9 11:01:55 CEST 2016
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.
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.
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 ?).
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 ?
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
> well, no, as Nk*Nb*Npw log(Npw) or Nk*Nb^2*Npw
>>> could you try to explain me how to reduce the computation
>> 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
+39-0432-558216 , fax +39-0432-558222 
Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Udine, via delle Scienze 208, 33100 Udine, Italy
+39-0432-558216, fax +39-0432-558222
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