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[TORRENT Marc <marc.torrent@cea.fr>]

Hi Zeila,

I'm not the band-fft expert but concerning PAW I can give some comments:
With a lot of atoms, PAW is still not fully efficient.
because it misses the parallelisation over atoms; this is 50% coded but not yet ready.
(Writing of the missing part is planed soon).

So, if you have a large number of atoms your computation could be slow because of MEMORY use.

You can try to reduce significantly the memory by setting:
pawstgylm 0
in your input file.

That's all I can say for now.

Of course, if the memory usage is not the origin of your slow behaviour, I let the LOBPCG experts answer...

Marc


PS: additional question: have your Broyden steps the same length in seq and paral mode ?
(I mean : the number of SCF cycles)


Le 01/12/10 13:32, Zeila Zanolli a écrit :

87F04E45-A4A9-4613-8410-549579560E1A@uclouvain.be" type="cite">Dear all,

I'm trying my luck with the relaxation of a ~60 atoms molecule with abinit with PAW.

I've set-up a calculation in serial mode and one in parallel mode, using the band/fft parallelization.

However, the parallel calculation is taking the same time as the serial one, as you can see here:

serial:    63 broyden steps in 41 hours

7 cpus:  64 broyden steps in 40 hours

I've set the parallel flags using the paral_kgp = -n 

I have also have a spin-polarized system and in this case the parallel calculation was not proceeding at all:

the calculation stopped at the broyden step 0, after the 3^rd iteration.

The serial calculation for the same spin-pol system is, instead, proceeding without problems (ok - it is just extremely slow: 19 broyden steps in ~ 40 hours).

Here are my input files:

#--------------- for the parallel calculation ---------------------

paral_kgb 1

npkpt  1

npband 7       

npfft  1  

bandpp 4

nband 112

wfoptalg 4  nloalg 4  fftalg 401  intxc 0  fft_opt_lob 2

#-------------- the following is the same in the parallel and serial calculation ------

kptopt 1

ngkpt 1 1 1

nshiftk 1

shiftk 0 0 0

ntime 1000

tolmxf 1.e-5

ionmov 2

tolrff 1.e-2

ixc 1

ecut 20

pawecutdg 40

nstep 100

diemac 1

Same input for the spin-polarized case, just with the 'spin' variables in addition:

nsppol 2

and initialization of the spin.

Any help is appreciated!

Thanks,

    Zeila

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Dr. Zeila Zanolli

Université Catholique de Louvain (UCL)

Unité Physico-Chimie et de Physique des Matériaux (PCPM) 

Place Croix du Sud, 1 (Boltzmann)

B-1348 Louvain-la-Neuve, Belgium

Phone: +32 (0)10 47 3501 

Mobile: +32 (0)487 556699

Fax: +32 (0)10 47 3452

e-mail: zeila.zanolli@uclouvain.be

web: http://www.nano2hybrids.net/

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