Structural evolution and phase transition mechanism of $$\hbox {MoSe}_2$$ MoSe 2 under high pressure

$$\hbox {MoSe}_2$$ is a layered transition-metal dichalcogenide (TMD) with outstanding electronic and optical properties, which is widely used in field-effect transistor (FET). Here the structural evolution and phase transition of $$\hbox {MoSe}_2$$ under high pressure are systematically studied by CALYPSO structural search method and first-principles calculations. The structural evolutions of $$\hbox {MoSe}_2$$ show that the ground state structure under ambient pressure is the experimentally observed P6 $$_3$$ /mmc phase, which transfers to R3m phase at 1.9 GPa. The trigonal R3m phase of $$\hbox {MoSe}_2$$ is stable up to 72.1 GPa, then, it transforms into a new P6 $$_3$$ /mmc phase with different atomic coordinates of Se atoms. This phase is extremely robust under ultrahigh pressure and finally changes to another trigonal R-3m phase under 491.1 GPa. The elastic constants and phonon dispersion curves indicate that the ambient pressure phase and three new high-pressure phases are all stable. The electronic band structure and projected density of states analyses reveal a pressure induced semiconducting to metallic transition under 72.1 GPa. These results offer a detailed structural evolution and phase diagram of $$\hbox {MoSe}_2$$ under high pressure, which may also provide insights for exploration other TMDs under ultrahigh pressure.