Density-functional study of magnetism in bare Au nanoclusters: Evidence of permanent size-dependent spin polarization without geometry relaxation

Abstract

Magnetism in bare uncapped gold nanoclusters is explored from a density-functional theory perspective with scalar relativistic effects included via the pseudopotential. The computed electronic structures of various nanoclusters reveal that permanent size-dependent spin polarization appears without geometry relaxation for bare clusters even though bulk gold is diamagnetic. The polarized ground states for clusters are favorable due to the hybridization of the $s$ and $d$ orbitals, and bare octahedral clusters are expected to be magnetic for cluster sizes of approximately 38 atoms and larger. Much larger clusters will be diamagnetic when the surface-to-volume ratio is small and the core diamagnetism prevails. Moderate changes in the interatomic distances and cluster geometry are shown not to alter this conclusion. Contrary to local-density approximation and embedded atom method predictions, generalized gradient approximation and hybrid geometry optimizations reveal increased interatomic bond distances in bare gold clusters relative to the bulk lattice values. In this case, optimization enhances the spin polarization.