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Research_

Hudson Group

Investigating problems in structural materials chemistry
Our group is interested in both understanding the underlying physical phenomena related to problems in structural materials chemistry, and improving the computational techniques used to simulate them.

Our aims

Our group works in a wide variety of systems, including:

  • liquid-solid interfaces in water-ice
  • defect migration in fusion reactor metals
  • solid-glass-solid interfaces in Si3N4¬†ceramics
  • other model network glasses such as amorphous silicon.

We use the following computational techniques:

  • Monte Carlo simulation (including kinetic MC and grand-canonical MC)
  • classical molecular dynamics
  • genetic algorithms.

Our research

The following descriptions are some honours projects examples and similar expanded topics are possible for PhD studies.

Predicting binary hard sphere phase diagrams

Hard sphere packing has obvious geometrical interest but it is also of relevance to colloidal crystals, which can display fascinating optical properties (eg. 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. This is why 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. This project aims 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.

The structure of amorphous solar cell materials

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 we 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. We will look at whether the germanium atoms segregate in the long term, or if this is a stable mixture. We'll also see how the composition fraction of germanium affects this.

How do network solids creep and crystallise?

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 we will explore both processes using a recently developed computer model.

Rearrangement mechanisms in supercooled liquid water

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 categorising topological rearrangements in networks. In this project we will analyse simulated liquid water trajectories from collaborators, in order to describe, categorise and understand the mechanistic processes going on in this important system.

Opportunities

For information about opportunities to work or collaborate with the Hudson Group, email Toby Hudson at toby.hudson@sydney.edu.au

Toby Hudson

Director of First Year Studies, Senior Lecturer in Theoretical Materials Chemistry
Address
  • Room 456, School of Chemistry Building (F11) University of Sydney NSW 2006