Joseph Nelson

In Plain English

The properties of a solid depend intimately on the exact arrangement of its consistuent atoms, and the strength of chemical bonding between those atoms. A very familiar example is carbon, where atoms can be arranged in 2D hexagonal sheets, creating a soft, flaky and opaque material (graphite), or with atoms in a 3D network, creating an extremely hard and transparent material (diamond). My research uses methods that allow us to predict the arrangement of atoms in a solid (its crystal structure) from first principles - that is, without recourse to any prior knowledge, other than the constituent atoms.

We can get some insight into the structure and properties of a solid by using basic chemistry. This supplies us with rules about the number and nature of chemical bonds that atoms form, based on their position in the periodic table - e.g., carbon likes to surround itself with four covalent bonds, oxygen two, and so on. However, a full and accurate description of the chemical bonding in a solid requires the laws of quantum mechanics. Given a particular crystal structure, my research uses a branch of quantum mechanics called density functional theory, which allows us to calculate how electrons are distributed in the structure. From this, we gain insights into the types of chemical bonding occuring in a solid, and we are also able to calculate a plethora of other properties such as mechanical strength, optical properties and electrical conductivity. I'm particularly interested in the behaviour of solids at very high pressures (such as those found at the center of the Earth), where unexpected behaviour can emerge and the rules of basic chemistry don't always apply.