## 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.