Joseph’s research is in the realm of materials modelling – using theoretical tools to model and predict the properties of materials. In particular, Joseph is interested in optical, thermal, and vibrational properties of systems, with a focus on large-scale or complex organic solids, such as organic semiconductors. His past work has focused on the vibrational properties of defects in diamond, minerals in the lower mantle, and the optical properties of molecules in solution. In his research, Joseph typically makes use of first principles materials modelling methods, i.e., those that aim to solve the equations of quantum mechanics. His work usually involves the workhorse of materials modelling, density functional theory, but often other methods as well. Joseph is not only interested in applying such methods to systems of interest, but also in developing them. He is an active developer of the linear scaling density functional theory code ONETEP, and has contributed to the CAESAR code for calculating anharmonic effects.