Escher, Susanne Gudrun Elisabeth Thea; (2020) Structure prediction of alkaline earth oxide nanoclusters in vacuo and on graphene. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Can nanoclusters be used in materials design?. Knowing the structure of nanoclusters can give insight into their properties, knowing which nanocluster sizes have only one stable structure can inform experiment and knowing their behaviour on a surface is important as they are expected to be stabilised in such an environment.In this thesis, an evolutionary algorithm has been used in conjunction with interatomic potentials and density functional theory to elucidate the structures of (BaO)n nanoclusters where n= 1 to 18 and 24. Then, data mining was used to find structures of strontium, calcium and magnesium oxides of the same sizes. It was found that for barium oxide clusters, sizes n= 4,6,8,10 and 16 are the best synthesis targets as they have one especially low-energy structure and are also relatively low energy compared to other sizes. Synthesis target sizes for the other three oxides were: sizes n= 9,15,16,18 and 24 for (MgO)n; sizes n= 8,9,12,16,18 and 24 for (CaO)n; and the greatest number of sizes for (SrO)n clusters (n= 8,9,10,12,13,15,16,18 and 24).Cuboid rocksalt cuts were particularly energetically favourable for barium, strontium and calcium oxides, and therefore these cuboids were looked at in greater detail. In particular, the influence of Madelung constants on their stability is investigated, and nanowire, slab and bulk energies are extrapolated from their energies.A set of interatomic potentials was developed to investigate the behaviour of these nanoclusters above a graphene surface, and their interaction with the surface was further looked into.

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