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Sydney University | School of Chemistry | |
| Dr Toby Hudson | |||
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My work uses computational methods to investigate problems in structural materials chemistry. I have an interest in both understanding the underlying physical phenomena, and improving the computational techniques utilised to simulate them.
I have worked in a wide variety of systems, including:
The computational techniques I have greatest expertise in are:
The descriptions below are written as honours projects, but similar expanded topics are possible for Ph.D. studies. Please contact me to discuss your interests in or near any of these fields.
Hard sphere packing has been an area of research since the days of stacking cannonballs. Apart from the obvious geometrical interest, it is of relevance to colloidal crystals, which can display fascinating optical properties (e.g. opals). To make predictions about the phase diagram, we need to know what solid phases are possible. At high pressures, dense phases will predominate, but which crystalline structures are densest? For systems with two different sizes of particles, the densest crystal structures depend on the size ratio, and are not always known. Thus, the hard sphere phase diagrams made to date were constructed using a few observed crystal structures as the only candidate solid phases. We recently performed a systematic search through known crystal structures, and found two more crystal structures to be denser than segregated fcc packing for binary spheres with a radius ratio around 0.5-0.6. Your project will be to include these structures when predicting a phase diagram. The project will involve a technique called thermodynamic integration to calculate and compare the free energies of each phase at each point on the phase diagram.
Amorphous networks made of a mixture between silicon and germanium have been suggested as night vision or solar cell materials. They are especially interesting because the bandgap, and hence the photoelectric properties can be tuned by varying the composition. The best available models for their structure consist of a random network topology generated with atoms of equal size (silicon), and then decorated with the differently sized silicon and germanium atoms. This ignores the possibility that the germanium atoms affect the topology of the network, that compositional ordering is linked to topological change. In this project you will study this effect using a Monte Carlo simulation which skips atomic vibrations and studies the evolution and equilibration of the system on the timescale of bond-rearrangements and atomic diffusion. Do the germanium atoms segregate in the long term, or is this a stable mixture? How does the composition fraction of germanium affect this?
Four coordinated network solids, such as silica and silicon, are important materials and, thanks to the low coordination, structurally simple. This makes them ideal places to start in understanding how solids, particularly ones without crystalline order, relax when stressed and initiate collective structural changes, like crystal growth. In this project you will explore both processes using a recently developed computer model.
Liquid water can be described as a continually rearranging network of hydrogen bonds. There is recent evidence that supercooled water can exist in two distinct liquid states, where the difference is clearly seen in the longevity and structure of the bonds in the network. We have recently developed a scheme for categorizing topological rearrangements in networks. In this project you will analyse simulated liquid water trajectories from collaborators, in order to describe, categorize and understand the mechanistic processes going on in this important system.