Abstract
On the basis of an unbiased structure prediction, it is shown that the stable form of NiSi under pressures of 100 and 200 GPa is the Pmmn structure. Furthermore, a new stable phase has been discovered: the deformed tetragonal CsCl-type structure with a = 2.174 angstrom and c = 2.69 angstrom at 400 GPa. Specifically, the sequence of high-pressure phase transitions is the following: the Pmmn structure below 213 GPa, the tetragonal CsCl type in the range 213-522 GPa, and cubic CsCl higher than 522 GPa. As the CsCl-type structure is considered as the model structure of the FeSi compound at the conditions of the Earth's core, this result implies restrictions on the Fe-Ni isomorphic miscibility in FeSi.