Ab initio study of structural stability of small 3$d$ late transition   metal clusters : Interplay of magnetization and hybridization
  Using first-principles density functional theory based calculations, we analyze the structural stability of small clusters of 3$d$ late transition metals. We consider the relative stability of the two structures - layer-like structure with hexagonal closed packed stacking and more compact structure of icosahedral symmetry. We find that the Co clusters show an unusual stability in hexagonal symmetry compared to the small clusters of other members which are found to stabilize in icosahedral symmetry based structure. Our study reveals that this is driven by the interplay between the magnetic energy gain and the gain in covalency through $s$-$d$ hybridization effect. Although we have focused our study primarily on clusters of size 19 atoms, we find that this behavior to be general for clusters having sizes between 15 and 20. 
Soumendu Datta, Mukul Kabir and Tanusri Saha-Dasgupta
cond-mat.mes-hall