Unraveling the Planar-Globular Transition in Gold Nanoclusters through Evolutionary Search

TL;DR

This study uses high-throughput DFT calculations and genetic algorithms to investigate the structural transition of gold nanoclusters from planar to globular, revealing a gradual transition influenced by van der Waals interactions and electronic effects.

Contribution

It provides a comprehensive computational analysis of over 20,000 gold nanoclusters, elucidating the factors influencing their structural transition from planar to globular forms.

Findings

The transition is gradual at room temperature.

Van der Waals interactions stabilize globular structures.

s-d hybridization alone does not determine planarity.

Abstract

Au nanoclusters are of technological relevance for catalysis, photonics, sensors, and of fundamental scientific interest owing to planar to globular structural transformation at an anomalously high number of atoms i.e. in the range 12-14. The nature and causes of this transition remain a mystery. In order to unravel this conundrum, high throughput density functional theory (DFT) calculations, coupled with a global structural optimization scheme based on a modified genetic algorithm (GA) are conducted. More than 20,000 Au$_{12}$, Au$_{13}$, and Au$_{14}$ nanoclusters are evaluated. With any DFT functional, globular and planar structures coexist across the size range of interest. The planar-globular transition is gradual at room temperature rather than a sharp transition as previously believed. The effects of anionicity, $\textit{s-d}$ band hybridization and long range interactions on the dimensional transition are quantified by using the structures adjacent to minima. Anionicity marginally changes the relative stability of the clusters. The degree of $\textit{s-d}$ hybridization is varied via changing the Hubbard U value which corroborate that $\textit{s-d}$ hybridization alone does not stabilize planar structures. van der Waals interactions, on the other hand, stabilize globular structures. These results elucidate the balance between the different reasons of the dimensional transition in gold nanoclusters.