High Pressure Phases

In the first paper, Pickard and Needs applied the AIRSS technique to high-pressure phases of silane [Phys. Rev. Lett. 97, 045504 (2006)], first showing that the AIRSS method works well by performing tests on silicon at zero pressure. They correctly found the four experimentally verified phases. They concluded that there is a metal phase of silane that could be obtained experimentally. This phase may be candidate for high temperature superconductivity. The high-pressure insulating I4₁/a phase predicted in this paper has been observed in the recent x-ray diffraction studies of Eremets et al. [Science 319, 1506 (2008)].

In [Phys. Rev. B 76, 144114 (2007)] a new phase of aluminium hydride that is metallic at sufficiently low pressures to be seen in a diamond anvil cell was predicted using AIRSS. The high-pressure metallic Pm-3n phase predicted in this paper has been observed in the recent x-ray diffraction studies of Goncharenko et al. [Phys. Rev. Lett. 100, 045504 (2008)].

Since this early work Pickard and Needs have applied the AIRSS method to a range of other high-pressure problems such as how calcium interlocates between graphene sheets [Phys. Rev. B 75, 085432 (2007)]: how hydrogen bonds at high pressure [Nature Physics 3, 473 (2007) ] : new phases of H₂O [J. Chem. Phys. 127, 244503 (2007) ], and interesting new phases of ammonia [Nature Materials 7, 775 (2008)], that form the rather unexpected NH^-₂ + NH⁺₄ ionic molecular crystals rather than a homogenous mix of NH₃.