[Pw_forum] testing HSE for BCC Fe

[Paolo Giannozzi]

On Fri, Sep 9, 2016 at 9:30 AM, Daniel Stoeffler <
daniel.stoeffler at ipcms.unistra.fr> wrote:

Surprisingly, the computation time is huge


no sir: "unsurprisingly" the computation time is huge. 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

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, fax +39-0432-558222
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