  A modified Metropolis atomistic simulation is proposed to model the structure
of grain boundaries (GBs) and interfaces in ionic nanostructured systems and is
applied to the magnetically interesting case of iron trifluoride (FeF3). We
chose long-range interatomic potentials adjusted on experimental results, and
adapted a previously established Monte Carlo scheme consisting of various
modifications of the simulated annealing/ Metropolis algorithm. Atomic
structures of twisted and tilted GBs as a function of the relative
disorientation of the grains have been achieved yielding close to
experimentally measured properties. This approach takes into account the
structure of the grains far from the interface in order to constrain the
relative orientation of the grains, without any periodic boundary conditions.
One concludes that a long-range coulombic falloff of the interatomic potentials
is necessary to obtain GB structures presenting a correct local topology but
with a smooth transition from crystalline to amorphous states. The structural
features are finally discussed in terms of topological aspects and local
magnetic structure.
