Using pair_style meam/c in parallel

    I wanted to use the MEAM potentials from the NIST database found here
    Interatomic Potentials Repository
    for my LAMMPS simulation, but even though I use the proper syntax (as far as
    I understand) for parallel use, the simulations take shockingly long and
    report only 100% CPU usage (instead of 1200%, as it should from these
    settings), task manager confirms those results, indicating it is running in
    a single-threaded manner.

please note, that you are trying to use OpenMP parallelism and not MPI
parallelism. pair style meam/c supports the only the latter (as do *all* styles
in LAMMPS) but not the former (as do only styles in USER-OMP, USER-INTEL, KOKKOS
if compiled accordingly and a few select other styles).

Although the density update loops could very well use OMP parallelism, which
would be noticeable especially with the higher cutoffs needed for proper 2NN
MEAM. I may implement this at some point, but won't get around to it anytime
soon, so if anyone wants to do it...

But in your example, I would still expect slightly more than 1 core due to the
multi-threaded neighbour list updates. Won't help a lot though.