Structure, bonding, and magnetism of small Fen, Con, and Nin clusters, n ≤ 5

Small clusters of iron, cobalt, and nickel were studied with all-electron density functional calculations using both local and generalized gradient approximations. The highly spin-polarized 3d4s electrons give rise to directional bonding, magnetism, and Jahn-Teller distortions, yielding structures where the bonding is maximized but high magnetic moments still remain, coupled ferromagnetically. The magnetization is enhanced relative to the bulk, in qualitative agreement with experimental data for clusters larger than fifty atoms. Short d-type bond lengths dominate for dimers and trimers. Both short (d-type) and longer 4s bonds occur for the tetramers. For the pentamers there are many single s bonds and the Re approach the bulk values.