Ab Initio Modeling and Molecular Mechanics Simulation of Nanoscale Systems
The outline of this project is to undertake a systematic survey of low energy structures of gold clusters using first principles techniques, or a combination of first principles and semi-empirical techniques. We aim to approach cluster sizes that are more realistic of those used in experimental set-ups or applications, that is clusters containing 100's or 1000's of atoms. The structure of gold clusters is still under debate. The difficulty of determining structure experimentally increases rapidly as the cluster size gets smaller, whereas the opposite is true for calculating structures. In addition in most practical situations the clusters are produced using wet chemical techniques that leave the nanoparticles with a molecular coating. These absorbed molecules may well play a significant role in determining the structure of the nanoparticle. We aim at initially modelling the interaction of simple molecules with high symmetry gold surfaces as a means of approaching the more complex problem of surface passivation of metallic clusters.
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Principal Investigator Mike FordInst. for Nanoscale Technology University of Technology, Sydney |
Project f64 |
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Co-Investigators Carl MasensBenjamin Soule De Bas Inst. for Nanoscale Technology University of Technology, Sydney |
RFCD Codes 291804, 240203, 250601 |
Significant Achievements, Anticipated Outcomes and Future Work
We have completed an ab initio survey of the low energy structures of bare gold clusters in the size range of 3 to 55 atoms and have mapped the potential energy surfaces extensively for the smaller clusters. The results suggest that the gold nanoparticles are disordered in this size range and that there are many closely spaced equilibrium structures accessible. The 2-D to 3-D structure transition occurs at 7 atoms, with 7 atom clusters being the first 3d structure. A study of the absorption energetics of benzene on the metallic Cu surface has been completed and the absorption orientation and energy determined. Simple thiols molecules absorbed onto the gold surface have been studied with absorption geometry and energy determined. In future work we intend to extend our gold cluster studies to larger clusters, more representative of those used in experiments, and to attempt to model the effects of surface absorbed molecules. This will require a combination of ab initio and molecular mechanics modelling.
Computational Techniques Used
We use two packages for this work: CRYSTAL98 and Siesta. They are both atomic orbital based first principles calculations. Both Hartree-Fock (HF) and Density Functional Theory (DFT) implementations are available in CRYSTAL98, whereas Siesta uses the DFT approach. Both packages have been used to perform total energy calculations to identify minimum energy structures. For the gold clusters calculations we have also written an empirical potential code to peform energy minimisations using a range of techniques.
Publications, Awards and External Funding
External Funding and Awards
None
Publications
11. B.L. Rogers, J.G. Shapter, and M.J. Ford, “Ab Initio Study of Benzene Absorption on the Cu(110) Surface and Simulation of STM Images”, Surf. Sci. 548 29 (2004).