2.1 Materials/Minerals under extreme condition

In physical science, extreme condition usually means the environment under extreme external parameters (i.e. high pressure, variable temperature, high radiation fluxes, strong electric/magnetic field, etc). Among all these physical variables, pressure perhaps possesses the greatest range - 60 orders of magnitude separate the pressure in the remotest vacuum of space from that found at the center of a neutron star. In the whole universe, most materials exist under high pressure (for instance, the center of the Earth is at a pressure of 350 GPa). Studies of high pressure behavior of the planetary materials are a key step to understand the formation structure and evolution of our Earth and other planets.

On the other hand, high pressure is considered to be a powerful tool to develop novel condensed states. It can be effective in shortening atomic distance, enhancing orbital overlap, and consequently modifying crystalline structures and tuning interactions, and eventually generating new states of materials different from normal compounds available at ambient conditions. For instance, pressure can substantially modify the electron correlation and electron-phonon interaction, giving rise to superconductivity in conventional materials ^{17; 18; 19}. The tendency towards electron delocalization under pressure leads many insulators, semiconductors and molecular crystals to become metals. Again, pressure is considered to be an important factor to synthesize superhard materials.

All the conventional researches on matters must start from the structural model. In experiment, the pressure range accessible in the laboratory is still rather limited, and the corresponding structural determination, characterization for a given materials under high pressure has been a long term challenge. Therefore, computational techniques are essential to understand materials under high pressure. A method which can predict stable and metastable structures given chemical composition and external conditions becomes increasingly demanded in high pressure science.