A Density Functional Study of Magnetism in Bare Gold Nano-clusters

TL;DR

This study uses density functional theory to show that bare gold nano-clusters can exhibit size-dependent magnetism due to s-d orbital hybridization, challenging previous predictions and highlighting the influence of surface effects.

Contribution

It provides a detailed DFT analysis demonstrating the emergence of magnetism in bare gold clusters and the impact of geometry and exchange-correlation functionals on their electronic structure.

Findings

Gold nano-clusters show size-dependent spin polarization.

Surface effects and orbital hybridization induce magnetism.

Geometry optimizations reveal increased inter-atomic distances and enhanced spin polarization.

Abstract

Magnetism in bare uncapped gold nano-clusters is explored from a density functional theory perspective with scalar relativistic effects included via the pseudo-potential. The computed electronic structures of various nano-clusters 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 inter-atomic distances and cluster geometry are shown not to alter this conclusion. Contrary to LDA and EAM predictions, GGA and hybrid geometry optimizations reveal increased inter-atomic bond distances in bare gold clusters relative to the bulk lattice values. This expansion enhances the preexisting spin polarization.