Transition metal oxides, such as TiO2, are promising materials for use in a number of emerging technologies – including photovoltaics and photocatalysis for water splitting and destruction of organic and biological contaminants. Realising the full potential of these materials will require careful tuning of their electronic, optical and chemical properties. Key to exerting this control will be a detailed understanding of the electronic structure of these materials.
Conventional computational methods allow access to bulk properties of materials – but struggle with simulation of large systems containing defects such as dopant atoms, vacancies, surfaces and grain boundaries – all features which greatly influence the performance of oxide materials in applications. Using linear scaling density functional theory I simulate large (thousand atom) systems, with a view to understanding how defects change (for better or worse) technologically relevant properties. Of particular interest is empowering experimentalists to readily identify defect types using spectroscopic methods such as electron energy loss spectroscopy (EELS) by producing predicted spectra for a wide suite of defect species.
In Plain English
Titanium dioxide (TiO2) is a rather unassuming compound, however it has risen to a position of ubiquity in our daily lives. You'll find it in white paint (often replacing toxic lead compounds), toothpaste, as an inert filler and pigment in tablets as well and many other applications: if a product you use is white – there's a reasonable chance there's some TiO2 in it. All of these uses rely on the 'boring' properties of TiO2 - it's not very reactive and doesn't interact much with visible light (this is why it looks white when ground into a powder).
In the last twenty years or so a different set of uses for TiO2 has been found. These exploit the fact that TiO2 can absorb ultraviolet light - modified versions are now frequently used in sunscreens. Even more exciting is the possibly of altering TiO2 so that it can absorb visible light too and use this energy to do useful things like turn water into fuel, generate electrical currents and destroy harmful pollutants and bacteria. Achieving these objectives will require a thorough understanding of TiO2 at an atomic level. To this end I run large computer simulations of TiO2 which I use to make predictions about how modifications to its structure will change its interaction with light and chemicals. I also predict how these changes might be measured in experiments – so people making modified TiO2 can know with confidence the atomic structure of the material they have made.