Based on the unbiased structure prediction, we showed that the stable form of NiSi compound under the pressure of 100 and 200 GPa is the Pmmn-structure. Furthermore, we discovered a new stable phase - the deformed tetragonal CsCl-type structure with
a = 2.174 {AA} and c = 2.69 {AA} 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 FeSi compound at the conditions of the Earths core, this result implies restrictions on the Fe-Ni isomorphic miscibility in FeSi.
