Structure Prediction and Bonding Analysis of B$_{18}$Ag$_2$ Clusters Featuring Double-Ring Motifs

TL;DR

This study uses DFT and global optimization to analyze the structure, electronic properties, and bonding of B18Ag2 clusters, revealing a stable double-ring structure with delocalized electrons and weak Ag-B interactions.

Contribution

It introduces the first detailed computational analysis of silver-doped boron clusters with double-ring motifs, highlighting the stabilizing role of Ag atoms and electron delocalization.

Findings

B18Ag2 has a bent double-ring structure as the global minimum.

Electronic excitations are delocalized within the boron framework.

Ag atoms stabilize the structure mainly through electrostatic interactions.

Abstract

The structural stability, electronic structure, and bonding characteristics of the silver-doped boron cluster B18Ag2 were investigated using density functional theory (DFT) combined with global optimization techniques. Basin-hopping searches identify a bent double-ring structure as the global minimum, consisting of two stacked B9 rings symmetrically stabilized by Ag atoms located above and below the boron framework. The UV-Vis absorption spectrum exhibits weak transitions in the near-infrared region and intense bands in the visible and near-ultraviolet regions, reflecting delocalized electronic excitations within the boron framework. Charge analysis indicates moderate electron redistribution from Ag atoms to the boron scaffold. Real-space bonding analyses based on the electron localization function (ELF), reduced density gradient (RDG), and molecular electrostatic potential (MEP) reveal that bonding is dominated by {$\sigma$}-delocalization over the boron skeleton, while Ag-B interactions are weak, non-directional, and primarily electrostatic. The continuous annular electron delocalization within the double-ring structure suggests an aromatic-like character. These findings establish B18Ag2 as a silver-stabilized boron double-ring cluster in which global electron delocalization governs structural stability, while Ag atoms act as axial stabilizing centers that modulate the electronic structure. This work provides new insight into the role of coinage-metal doping in stabilizing extended boron nanostructures.