The harmonic theory of lattice dynamics is the starting point of the description of phonons in a crystal and works well for many systems.  However, the assumption that the interatomic potential is harmonic does not capture effects such as thermal expansion or thermal conductivity.  Additionally, the harmonic approximation is not valid for many materials such as lead telluride - a promising thermoelectric material - where anharmonic effects play a significatnt role in the lattice dynamics and thus the thermal properties of the material.

In order to better understand these materials, it is therefore necessary to extend the harmonic theory and investigate the anharmonic terms of the interatomic potential.  My research aims to do this through the construction of empirical interatomic potentials from first-principles calculations and optimisation of these potentials on the basis of thermal diffuse scattering data from x-ray diffraction experiments.