[QE-users] pw.x -nt X, optimization at GGA and Hybrid calculations

[Pietro Bonfa']

Dear Lucas,

there was indeed a bug with taskgroups in v 6.1, fixed in v6.2 (see 
release notes: 
https://gitlab.com/QEF/q-e/blob/develop/Doc/release-notes#L338 ).

Some time ago I gave a presentation about the parallelization scheme of 
QE. Unfortunately the session was not recorded but you may extract some 
information from the slides: https://tinyurl.com/y3qb7jql .

Hope this helps,
best regards,
Pietro

On 5/9/19 6:43 PM, Lucas Nicolás Lodeiro Moraga wrote:
> Hi all!
> 
> I am performing a scaling test with QE (versions 6.1 and 6.3) for a big 
> sistem >2000 electrons with GGA/USPP. I found that when I use more than 
> one node the use of -nt is very usefull to improve the calculation time. 
> For this system nt=number of nodes is the best choise in most cases... 
> but sometimes nt = number of nodes + X, with X = 1,2,3,4... (no more 
> than 4) is better. As an example, if i use 440 processors, with 44 
> processors nodes, the best nt is 11.
> Also, I read that the -nt is usefull when the FFT 3D grid < n° 
> processors, but in some cases when FFT 3D grid > n° processors, -nt 2 or 
> 3 improves the calculation too.
> Can someone help me with this topic, give me more information and 
> internalize me in this topic?
> 
> On the other hand, I try this with hybrid functional in a simple 
> semiconductor sistem with ~50 atoms with HSE/NCPP. With 6.1 version the 
> calculation CRASH when I use -nt 2, the error message is:
>       iteration #  1     ecut=    80.00 Ry     beta=0.30
>       Davidson diagonalization with overlap
>       ethr =  1.00E-02,  avg # of iterations =  8.0
> 
>       negative rho (up, down):  1.101E-01 0.000E+00
> 
> 
>   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>       Error in routine electrons (1):
>       charge is wrong: smearing is needed
>   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> 
>       stopping ...
> 
> When I use smearing:
>       iteration #  1     ecut=    80.00 Ry     beta=0.30
>       Davidson diagonalization with overlap
>       ethr =  1.00E-02,  avg # of iterations =  8.0
> 
>       negative rho (up, down):  1.081E-01 0.000E+00
> 
>       total cpu time spent up to now is       24.5 secs
> 
>       WARNING: integrated charge=   312.31515712, expected=   320.00000000
> 
>   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>       Error in routine electrons (1):
>       charge is wrong
>   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> 
>       stopping ...
> 
> It is very weird, and with 6.3 version the calculation runs without 
> problem, but take more time, and the speedup is very very low in 
> comparison with one node calculation.
> There is a bug in 6.1 version? Is it a bug in the 6.1 compilation?
> Somebody knows some method to accelerate the hybrid calculations to be 
> able to occupy more nodes?
> 
> Regards
> 
> Lucas Lodeiro
> Universidad de Chile
> 
> 
> 
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-- 
Pietro Bonfa'
Dipartimento di Scienze Matematiche, Fisiche e Informatiche
Parco Area delle Scienze, 7/A
43124 Parma