Can package manager version of NWChem be run in parallel?

[Scott Muller]

Hello

I'm trying to run NWChem in parallel on WSL (using Ubuntu 20.04.1). I successfully installed NWChem via the instructions on the website. NWChem works fine in serial using the command

$ nwchem input.nw > output.nw

I run into problems when I try to run NWChem in parallel using the command

$ mpirun -np 4 nwchem input.nw > output.nw

The job runs, but in the Job information section near the top of output.nw I have "nproc = 1", the same as in serial. In the website instructions for compiling NWChem from source it says that USE_MPI needs to be set to "y". Since I used Ubuntu's package manager to install NWChem, I never specified this option. Is this installation of NWChem capable of being run in parallel, or do I need to compile NWChem from source to get this feature? Is there a place where the options for the package manager version of NWChem for WSL are specified? (If this version only works in serial, that information should probably be present in the instructions on the website.) If it can be run in parallel, are there special environment variables that need to be specified for it to work?

Thanks,

Scott

[Edoardo Aprà]

Since the Ubuntu packed version of NWChem is compiled using OpenMPI, you must use mpirun from OpenMPI (and not from Mpich, for example).

The name of the OpenMPI mpirun command is

/usr/bin/mpirun.openmpi

if this command has not been installed yet, you can install it with the apt command

sudo apt install openmpi-bin

The command for running NWChem becomes

/usr/bin/mpirun.openmpi -np 2 nwchem test.nw  > test.out

[Scott Muller]

Excellent! That completely solved my problem. Thank you very much!