Theoretical studies of free and supported nanoalloy clusters

Ismail, Ramli (2013). Theoretical studies of free and supported nanoalloy clusters. University of Birmingham. Ph.D.

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Abstract

Nanoclusters offer unique physical and chemical behaviour, with the possibility of fine-tuning size and structures. Detailed theoretical studies can extend our understanding of these complicated systems. In this research, a good balance between accuracy and computational cost in describing electronic structure was sought via a combined Empirical Potential (EP) - Density Functional Theory (DFT) method. Global optimisation searches were performed using the Birmingham Cluster Genetic Algorithm and Basin-Hopping Monte Carlo algorithm coupled with the semi-empirical Gupta potentials. The sensitivity of the potentials was further studied for various potential parameterisations. Exploration of Pd-Au, Pd-Pt and Ni-Al clusters evidence the polyicosahedra – decahedra – face-centered cubic transitions, but below 50 atoms, these motifs are energetically very competitive, which led to a detailed structural study for the 34- and 38-atom clusters, as a function of composition. A qualitatively good agreement between EP and DFT was found, with a prevalence towards coreshell Dh\(_3\)\(_4\) and TO\(_3\)\(_8\) structure for Pd-Au and Pd-Pt clusters. The performance of empirical calculations varies with composition. On an MgO support, Pd-Au clusters showed significant size and composition effects. Consistent with the available experimental findings, Pd atoms preferentially bind to the oxygen sites at the interface and good cluster-substrate epitaxy was observed.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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