Reactive
force field molecular dynamics is a powerful tool to simulate
large-scale reactive events such as catalytic reactions and metallic
corrosion, including the carburization or so-called metal dusting
corrosion. Building on a vast set of reactive force field parameters,
it aims to reduce the gap between computational and experimental observations.
However, the production of different versions of reactive force field
parameter sets in the past 2 decades demonstrates the challenges faced
by developers when attempting to describe correctly and at the same
time a broad range of environments, such as the kinetics of CO adsorption,
dissociation, and carbon diffusion in iron systems. This has limited
the ability of these force fields to capture the competing phenomena
governing complex evolution such as the carburization of iron responsible
for metal dusting corrosion. In this work, we demonstrate that it
is possible to treat very different environments in an integrated
way by expanding the ReaxFF parameter set, creating an environment-specific
description. This approach enables us to capture both metallic surface-induced
dissociation of carbon-containing gases such as carbon monoxide (CO)
and atomic carbon bulk diffusion in iron systems within the same simulation
setup so far unreachable with previously available force fields. Employing
this extended-ReaxFF to describe a cell containing a gas mixture of
carbon monoxide and argon reacting with an Fe(110) surface, we fully
capture at the same time competing carburization reaction/diffusion
processes on both the surface and the bulk. Analysis of the radial
distribution function and charge density maps shows a variety of carbon
bonds at different stages/layers, highlighting the diversity of the
mechanisms captured while using our extended-ReaxFF. Interestingly,
at a CO coverage higher than 0.7 monolayers, the atomic arrangement
of the iron atoms is sufficiently altered to cause surface reconstruction
leading to a significant increase in carbon diffusion. Moreover, we
are able to observe and quantify the diffusion of Fe from the bulk
toward the upper coke layer, computationally elucidating the slow
but continuous coke formation reported experimentally, opening a wide
range of opportunities to model various stages of iron carburization
mechanisms.