[Pw_forum] Low speed

[Paolo Giannozzi]

On May 12, 2010, at 21:07 , mohsen modaresi wrote:

> 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?

it depends. There are two separate issues to be considered:
- serial speed, i.e. the speed of a single processors, and
- effectiveness of parallelization.
For the former, you need fast mathematical libraries and a
decent compiler. For the latter, you need to have an idea of
how parallelism in QE works, then to perform some tests.
QE is carefully parallelized, but don't assume that running
on 8  processors (especially of multicore machines)
guarantees running in 1/8 of the time.

P.
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Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222