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GAMESS-US: Difference between revisions
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→Running GAMESS on multiple CPUs
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GAMESS calculations can make use of more than one CPU. The number of CPUs | GAMESS calculations can make use of more than one CPU. The number of CPUs | ||
available for a calculation is determined by the <code>--cpus-per-task</code> | available for a calculation is determined by the <code>--cpus-per-task</code> | ||
setting in the | setting in the job script. | ||
As GAMESS has been built using | |||
use CPU cores that are located on the same compute node | As GAMESS has been built using [https://en.wikipedia.org/wiki/Unix_domain_socket sockets] for parallelization, it can only | ||
use CPU cores that are located on the same compute node. Therefore | |||
the maximum number of CPU cores that can be used for a job is dictated by | the maximum number of CPU cores that can be used for a job is dictated by | ||
the | the size of the nodes in the cluster, e.g. 32 CPU cores per node on [[Graham]]. | ||
Quantum chemistry calculations are known to not scale | Quantum chemistry calculations are known to not scale well to large numbers | ||
of CPUs as compared to e.g. classical molecular mechanics, which means | |||
that they can't use large numbers of CPUs efficiently. Exactly how many | that they can't use large numbers of CPUs efficiently. Exactly how many | ||
CPUs can be | CPUs can be used efficiently depends on the number of atoms, the number of | ||
number of atoms, number of basis functions and level of theory | basis functions, and the level of theory. | ||
To determine a reasonable number of CPUs to use, one needs to run a scaling | To determine a reasonable number of CPUs to use, one needs to run a scaling | ||
test - | test--- That is, run the same input file using different numbers of CPUs | ||
and | and compare the execution times. Ideally the execution time should be half | ||
as long when using twice as many CPUs | as long when using twice as many CPUs. Obviously it is not a good use of | ||
Obviously it is not a good use of resources | resources if a calculation runs (for example) only 30% | ||
faster when | faster when the number of CPUs is doubled. It is even possible for certain | ||
calculations to run slower when increasing the number of CPUs. | |||
=== Memory === | === Memory === | ||