Computational Modelling of Nanomaterials - PhD Projects Available

I will not be recruiting MPhil/PhD students to start in October 2015, as I will be leaving Cambridge in February to move to Warwick. I would encourage anyone interested in working with me there to get in touch and discuss possible projects. Alternatively, if you are keen to study large-scale electronic structure methods specifically in Cambridge, one way to do so would be to apply to the Centre for Doctoral Training in Computational Methods for Materials Science. This includes a 1-year MPhil followed by a 3-year PhD. Another possibility is an application to the Winton Programme for the Physics of Sustainability for a prestigious Winton Scholarship

Overview of my research
Nanomaterials offer us exciting new ways to control material properties, by varying material attributes why are not available in bulk systems. For example, in nanocrystals, growth conditions can be tuned to vary particle size, shape, surface terminations, composition and defect structure, and in an aggregate of nanocrystals, alignment, mutual interactions and interations with a solvent come into play. Nanomaterials are thus the key to making a success of many emerging technologies, such as Photovoltaics and Photocatalysis (means of turning light from the sun into other useful forms of energy). However, while these variable design factors enable these applications, they also result in a vast phase space one might need to explore in order to design optimal materials for a given purpose. Fortunately, we are able to explore this space without the expense and difficulty of experiments by using computational simulation! Computational "experiments" based on simulation of realistic structures can be used to examine the various factors influencing a such as optical absorption, and disaggregate the factors influencing it in a way which is impossible in the complex, noisy and messy world of experiments!

1) Methodological Development for Nanomaterials Simulation
Along with other academics at Cambridge, Imperial and Southampton, I am an author of the ONETEP Linear-Scaling Density Functional Theory (DFT) Code . The computational effort involved in traditional approaches to DFT scales cubically with system size, placing a barrier to calculations of more than a few thousand atoms. Linear-Scaling approaches to DFT, of which ONETEP is one of only a few practical examples worldwide, use methods based on local orbitals to avoid the cubic scaling steps and thus scale linearly with system size, allowing first-principles simulation of systems of many thousands of atoms. However, solving for the electronic states, and the total energy is just the start of what is possible. To actually use these techniques to assist in the interpretation of experimental results, we need to be able to determine the response of a system to external perturbations such as applied electronic fields or displacements of each atom.
A highly-motivated student with strong computational and mathematical skills is sought, to embark on a project to develop methodology to perform so-called "linear-response" calculations with ONETEP. This methodology can be used to accurately calculate the response of a systems such as a nanocrystals, to a these types of perturbations. This would enable a range of exciting new types of calculation, principally relating to the crucial topic vibrational spectroscopy: IR spectra, electron- phonon coupling, and many more. Applications would be to nanocrystal and organic crystal systems of interest to photovoltaic applications (see below).

2) Large scale ab initio simulations of metallic nanoparticles: method development and applications
In collaboration with Shell Technology Centre, Bangalore
Shell PI: Leonardo Spanu
The physical and chemical properties of transition metal nanoparticles are of great interest for several industrial applications (e.g. catalysis, magnetic materials), since nanoparticles often exhibit characteristic that are significantly different compared to bulk materials. An accurate description of the electronic structure is often required to predict properties at the nanoscale. Electronic properties of systems containing up to few thousand atoms can be successfully described using Density Functional Theory. Unfortunately, DFT calculations suffer from an unfavorable scaling and the simulation of metallic systems of several nanometers is not possible. This PhD project proposes to investigate the limits of existing approaches and to develop new methods for large scale simulations of metallic systems (several thousand of atoms). Possible area of interest includes (but is not limited to) order-N methods for system with a vanishing band gap, new algorithms for energy minimization, mixed quantum-classical approaches.

3) Computational Simulation of TiO2 Nanocrystals
TiO2 is at the heart of a wide range of photoactive devices: dye-sensitized solar cells, water-splitting photocatalysts, and many more. However, in its usual bulk crystalline forms, TiO2 absorbs only a small fraction of the solar spectrum. Nanostructuring, ie creating materials with structure on the nanoscale, via the very wide range of options available in processing and treatment, can result in materials with very different (and considerably enhanced) properties compared to the bulk. For example, nanocrystalline TiO2 generally occurs in the anatase (rather than rutile) phase, rather than the usual rutile. Simulation of whole realistic nanocrystals using ONETEP opens up many new vistas for understanding and controlling the properties of TiO2-based nanomaterials. A PhD project is proposed to investigate this, requiring a student with a strong interest in computational simulation and solar energy production. Examples of topics to be studied would include "black" TiO2, the influence of water on the surface bandstructure of TiO2, and photocatalytic reactions on the surfaces of TiO2 nanostructures.