Basically if you have the hostnames in a hostfile.txt:
optistruct input.fem –hostfile ./hostfile.txt [-np <NUMBER OF MPI PROCESSES>] [-mpi <i|pl>]
The input files must be available from all nodes in the same path. This can be done by copying the input files to identical paths on all nodes or mount the folder containing the input files to all nodes.
Scratch files ought to be written to local high performance disk on each node.
Please check advanced installation guide for more details.