Structures and Stabilities: Quantum-Chemical Study of Aun (n = 2-2016) Nanoclusters by Extended Huckel and DFT Approaches

Bakhtiyor      Rasulev; Marquita      Watkins; Melissa      Theodore; Joany      Jackman; Jerzy      Leszczynski

Abstract

A fundamental understanding of the physical and chemical properties of gold clusters, namely, the size dependence of these properties, is necessary for developing wide range of gold clusters’ applications. Having this purpose in mind, the structural and energetic properties, such as binding energies, relative stability and band gaps ΔEHL (HOMOLUMO gaps) are evaluated. The gold clusters in a wide range of sizes, Aun (n=2 - 2016), were constructed and studied by Density Functional Theory and Extended Hückel Theory approaches. It was shown that the high values of ΔEHL for the clusters with n= 2, 6, 8, 20 correlate with the highest stability. This finding explains the existence of magic numbers for gold clusters. The 20 atom tetrahedral cluster stands out as particularly stable, comparing to the other small clusters. The binding energy EB is found to increase with the cluster size. The second difference in energy - Δ2E(n) value is used as the criterion of stability, in addition to ΔEHL and also shows a tendency to increase with the cluster size. This behavior suggests a transition of larger clusters towards bulk metallic properties. Both curves - Δ2E(n) and ΔEHL show sharp transformation from high values to close to 0 eV at n=252-504 cluster sizes (it relates to ca 2 nm cluster size).

Keywords: Gold, Clusters, ab initio, Hückel, DFT, Nanoparticle, Modeling.