Segregation and ordering in binary transition metal clusters

Abstract

Quantum mechanical calculations on 13 and 55-atom Fe–Ni clusters with icosahedral geometry have been performed using density functional theory (DFT) and a generalised gradient approximation (GGA) based exchange and correlation functional. It is observed that in the lowest-energy isomers found for both system sizes and all studied compositions, Fe atoms occupy the central position. Ni atoms, however, are scattered to maximise the number of Fe–Ni bonds, and thus segregate to the surface. The mixing energy for icosahedral clusters, with respect to composition, shows a similar trend as in bulk.