  Diffusion of interstitial alloying elements like H, O, C, and N in metals and
their continuous relocation and interactions with their microstructures have
crucial influences on metals properties. However, besides limitations in
experimental tools in capturing these mechanisms, the inefficiency of numerical
tools also inhibits modeling efforts. Here, we present an efficient framework
to perform hybrid grand canonical Monte Carlo and molecular dynamics
simulations that allow for parallel insertion/deletion of Monte Carlo moves. A
new methodology for calculation of the energy difference at trial moves that
can be applied to many-body potentials as well as pair ones is a primary
feature of our implementation. We study H diffusion in Fe (ferrite phase) and
Ni polycrystalline samples to demonstrate the efficiency and scalability of the
algorithm and its application. The computational cost of using our framework
for half a million atoms is a factor of 250 less than the cost of using
existing libraries.
