MOLPRO

2 RUNNING MOLPRO 6
Note that options --multiple-helper-server, --node-helper-server,
--single-helper-server, and --no-helper-server are only effective for MOL-
PRO built with MPI-2 library. In the cases of one or more helper servers enabled, one or more
processes act as data helper servers, and the rest processes are used for computation. Even so, it
is quite competitive in performance when it is run with a large number of processes. In the case
of helper server disabled, all processes are used for computation; however, the performance may
not be good because of the poor performance of some existing implementations of the MPI-2
standard for one-sided operations.
In addition, for MOLPRO built with GA library (TCGMSG MPI or MPI over InfiniBand), GA
data structures can’t be too large (e.g., 2GB per node) when running molpro job on multiple
nodes. In this case, setting environment variable ARMCI DEFAULT SHMMAX might be helpful.
The number should be less than 2GB (e.g., to set 1600MB for ARMCI DEFAULT SHMMAX
in bash: export ARMCI DEFAULT SHMMAX=1600). One can also use more computer nodes
to run such jobs, thus allocated memory for GA data structures on each node becomes smaller.
There is no such restriction for MPI-2 version of MOLPRO.