Intriguing structures and magic sizes of heavy noble metal nanoclusters around size 55 governed by relativistic effect and covalent bonding

Abstract

© 2015 AIP Publishing LLC. Nanoclusters usually display exotic physical and chemical properties due to their intriguing geometric structures in contrast to their bulk counterparts. By means of first-principles calculations within density functional theory, we find that heavy noble metal PtNnanoclusters around the size N = 55 begin to prefer an open configuration, rather than previously reported close-packed icosahedron or core-shell structures. Particularly, for PtN, the widely supposed icosahedronal magic cluster is changed to a three-atomic-layered structure with D6hsymmetry, which can be well addressed by our recently established generalized Wulff construction principle (GWCP). However, the magic number of PtNclusters around 55 is shifted to a new odd number of 57. The high symmetric three-layered Pt57motif is mainly stabilized by the enhanced covalent bonding contributed by both spin-orbital coupling effect and the open d orbital (5d96s1) of Pt, which result in a delicate balance between the enhanced Pt-Pt covalent bonding of the interlayers and negligible d dangling bonds on the cluster edges. These findings about PtNclusters are also applicable to IrNclusters, but qualitatively different from their earlier neighboring element Os and their later neighboring element Au. The magic numbers for Os and Au are even, being 56 and 58, respectively. The findings of the new odd magic number 57 are the important supplementary of the recently established GWCP.