[DFTB-Plus-User] Problem of parallel computing with openmpi

[Bálint Aradi]

Dear Tatsu,

> When I perform a MD calculation on 4 cores in one node, computational
> time effectively decreases compared to a single-core calculation.
> However, when the same MD calculation is done on 8 cores of two nodes,
> its computational time become 2-3 times longer than the case of 4 cores
> in one node.
> 
> I think that the calculated simulation box contains relatively a large
> number of atoms (496 Si atoms) and the number of nodes is just two, and
> thus communication overhead is not a cause. Would you give me advice
> about possible causes of this problem?
> 

It depends pretty much on the interconnect between your nodes. I could
get 1000 atoms scaling up to 4 nodes, when using nodes with 8 cores each
and connected by infiniband. Your system is rather small (you have
roughly half of the orbitals I used), but I still would accept scaling
to 2 nodes, provided you have a low latency interconnect.

  Best regards,

  Bálint

-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/cms/people/b-aradi/


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