Exploring the Interface Between Two Nanoclusters: Insights from Computational Methods

Aggregation of gold nanoclusters (GNCs) with desired properties requires detailed knowledge about the inter-cluster interface and its properties. The stability of [Au6]2 dimeric cluster configuration has been confirmed based on molecular dynamic simulation at 298 K temperature, 1 atm pressure, and water as solvent. The structural and electronic properties of series of monomeric and dimeric [Au6]2, [Au6H]2, [Au6CH3]2, [Au6C2H5]2, [Au6C5H9]2, [Au6C6H11]2, [Au6C6H5]2, [Au6C6H4CH3]2, [Au6C6H4CH3]2, [Au6C2H]2, [Au6C2CH3]2 and [Au6C2C6H5]2 clusters were studied using three different functionals in density functional theoretical methods by considering three different interfaces. The dimerization was found to alter the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap depending upon the interface between the clusters. The computation predicts that the presence of ligand-ligand (ML-LM) and ligand-metal (ML-ML) interfaces in ligated cluster dimers were found to decrease the HOMO-LUMO gap while the metal-metal (LM-ML) interface leads to larger cluster formations. The change in electronic structures is found to be the reflection of symmetry in the eigenfunctions. The vertical plane of symmetry at the ML-LM interface leads to a smaller HOMO-LUMO gap as a result of degenerate orbitals between the monomeric units. The distortion from the reflection symmetry at the ML-ML interface removes the degeneracy by splitting the orbitals which increases the HOMO-LUMO gap in the ligated clusters. Among the studied ligated nanoclusters, experimentally realized [Au6C2C6H5]2 possesses a small HOMO-LUMO gap. All the interfaces are found to behave similarly in the presence of various uniform electric fields. The consequences of HOMO-LUMO gaps were observed in redox parameters, and absorption properties and have been explained using molecular orbital plots.