[Pw_forum] Low speed

[O. Baris Malcioglu]

Dear Mohsen,
Please notice that you have asked a rather vague question regarding performance,

First of all, please notice that since PW is a plane wave code, it is
not just the number of atoms that determine the "size" of the system.
You have to take into account the number of plane waves you are using.
This depends on your cutoffs and simulation supercell. Exaggerating
the situation unnecessarily, for example putting only an ethane
molecule in a 500x500x500 Bohr box (even with modest cutoff) will
result in a system size that will certainly give a hard time to the
computer you are describing. In the same sense, using very high
cutoffs will lead to same problem.

Secondly, "3 hours" is not a good enough criteria, how many scf steps
do you perform in these 3 hours? Does your system have some
convergence problems?

Finally, 8 cpu is not a good enough identification nowadays, if the
"cpu" you are mentioning is due to hyper-threading, it is usually
better if you use only 4, since you waste your precious memory
bandwidth. This is especially important if you are using a low memory
bandwidth architecture.

Some general guidelines :

-Make sure that your computer is not using swap,
-Use architecture dependent acceleration libraries such as MKL. For
example you can setup fftw 3.x to utilize instruction sets such as
sse2.
-If this is a parallel compiler check wall times, how much do you
loose communicating?

Best,
Baris

2010/5/20 Phillip Nyawere <pnyawere at gmail.com>:
> You need high speed computer. I tried with 96 atoms and it was taking even
> longer.
> Success.
>
> On Wed, May 12, 2010 at 10:07 PM, mohsen modaresi
> <modaresi.mohsen at gmail.com> wrote:
>>
>> Dear Developers and users,
>> I run a SCF calculation with 71 atoms on a camputer with 8 cpu and 8GB
>> RAM, i expect it run in some minutes, But it take 3 hours to run.
>> Is it regular?
>>
>>
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>
>
>
> --
> Phillip W. Otieno Nyawere,
> Kabarak University,
> Dept of Physics & Mathematics,
> P.O Box Private Bag - 20157,
> Kabarak, Kenya.
> Tel +254728342054
> pnyawere at gmail.com, potieno at kabarak.ac.ke
>
> The battle belongs to the Lord.
>
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