Pressure possesses perhaps the greatest range of all the physical variables - 60 orders of magnitude separate the pressure in the remotest vacuum of space from that found at the centre of a neutron star. The centre of the Earth is at a pressure of 350GPa (3.5 million atmospheres) and more than 90% of the matter in the solar system exists at pressures above 100GPa. Pressure thus shapes the stars and planets, and fashions the continents and oceans. It can convert everyday liquids into spectacular crystals and turn common gases such as O2 into exotic metals. And it can convert coal into diamonds. Today, the maximum static pressure obtainable in the laboratory is several million atmospheres, while dynamic pressures as high as 1014 atmospheres have been created in thermonuclear explosions (such projects do NOT, however, form part of our PhD programme!). The pressure range presently accessible in the laboratory now approaches a remarkable 30 orders of magnitude.
Over the past 15-20 years, the condensed matter physics group of The University of Edinburgh has come to prominence for world-leading structural research at high-pressures. The physical properties of materials depend strongly on structure and interatomic distances. Since pressure can vary these distances considerably more than, say, temperature, it provides an extremely powerful means of examining the relationship between structure and properties - both towards a better fundamental understanding of the underlying phenomena and also for the improved design of applied materials. Additionally, pressure is a 'clean' variable in that it can bring about large changes in structure and properties without altering the chemical composition or thermal energy of a system. This makes high-pressure systems particularly amenable to computational study, and there is a vigorous international programme of ab initio all-electron calculations of high-pressure structural stability.
