Error with using alias for executable with mpirun/mpiexec

I have set up an alias for my LAMMPS executable, lmp_mpi, in my .zshrc file. Using just the alias on its own works fine, but when coupled with mpirun/mpiexec, which have worked previously when I just used the file path for lmp_mpi instead of the alias, I get the following error:

Input: mpirun -np 2 lammps -in in.fileName

Output:

> mpiexec was unable to find the specified executable file, and
> therefore did not launch the job. This error was first reported for
> process rank 0; it may have occurred for other processes as well.
>
> NOTE: A common cause for this error is misspelling a mpiexec command
> line parameter option (remember that mpiexec interprets the first
> unrecognized command line token as the executable).
>
> Node: dhcp-vl2041-10441 Executable: lammps

This has been a headache for me to resolve. My most straightforward guess is mpirun/mpiexec don't recognize the alias, but I am not quite sure. Any input would be appreciated.

I have verified that my alias for LAMMPS does work, listed as the following:

> alias
> lammps='/Users/myname/Documents/Project_Packages/lammps-23Jun2022/src/lmp_mpi'

And when I run just the alias, the executable is run on the command window.

I have read a lot on alias, but I haven't quite found a similar issue, especially with LAMMPS.

Try changing the alias to a 'global' alias with -g:

alias -g lammps='/Users/myname/Documents/Project_Packages/lammps-23Jun2022/src/lmp_mpi'

Aliases are just simple text substitutions. With a normal alias, i.e. without the -g, only the first token in a line is substituted. A global alias will be expanded anywhere it appears as a distinct token in the command line, e.g.:

> alias xyz='some longer text'
> print xyz
xyz
> alias -g xyz='some longer text'
> print xyz
some longer text
> print wxyz
wxyz

With the -g alias for lammps, the fully-expanded path will be passed to mpirun. The alias may also end up being expanded in unexpected situations, so it's usually best to use fairly unique names for global aliases.