Structure and magnetism in iron clusters

We present a general overview about existing experimental and theoretical works on structural and magnetic properties of small iron clusters in order to get a deeper understanding of the quantum effects which govern the dependence of their physical and chemical properties in the nanometer range. We find that experimental information on structure and morphology of the clusters is very limited, while there is a considerable amount of studies related to magnetic and electronic properties. Calculations based on first principles have been performed by a number of groups using different approaches to describe exchange and correlation effects. There is, however, serious disagreement among them regarding important cluster properties like magnetic moments and ground state geometries even of the smallest possible entities. We show that this can be partly traced back to the degree of symmetry imposed during the calculations, because it turns out that especially the magnetic moments are strongly dependent on cluster geometry. From our calculations we find that energetic ground states are characterized by distorted shapes for all cluster sizes considered. It is concluded that in order to obtain reliable values for the ground state properties of iron clusters, one has to consider regions of the potential energy surfaces belonging to unsymmetrical arrangements of the atoms and to allow for full relaxation of the atoms during the simulation.