  Global minimum structures of neutral (Fe2O3)n clusters with n = 1-5 were
determined employing the genetic algorithm in combination with ab initio
parameterized interatomic potentials and subsequent refinement at the density
functional theory level. Systematic investigations of magnetic configurations
of the clusters using a broken symmetry approach reveal antiferromagnetic and
ferrimagnetic ground states. Whereas (Fe2O3)n clusters with n = 2-5 contain
exclusively Fe3+, Fe2O3 was found to be a special case formally containing both
Fe2+ and Fe3+. Calculated magnetic coupling constants revealed predominantly
strong antiferromagnetic interactions, which exceed bulk values found in
hematite. The precise magnetization (spin) state of the clusters has only small
influence on their geometric structure. Starting from n = 4 also the relative
energies of different cluster isomers are only weakly influenced by their
magnetic configuration. These findings are important for simulations of larger
(Fe2O3)n clusters and nanoparticles.
