Structure and spin in small iron clusters

Density functional calculations have been performed for iron clusters with up to seven atoms. The electron-ion interaction is treated by a pseudopotential, and the large effect of core electrons on the spin configuration by modifying the exchange-correlation function. The scheme allows us to perform molecular dynamics (MD, Car-Parrinello) simulations and to explore the potential energy surface of the cluster without symmetry or other constraints. The most stable structures have magnetic moments ≈3μB per atom and are generally compact. We discuss the structural trends, particularly the similarities with the close-packed structures found in clusters where the atoms interact with a pairwise Lennard-Jones potential.