Ab initio phase diagram of WSe based on crystal structure prediction

In order to seek for photoelectric and thermoelectric materials, we have performed the crystal structure search for transition metal chalcogenides of WSe using the advanced crystal structure prediction algorithms combined with ab initio calculations. After globally optimization and search for the crystal structures of WSe under different pressures, three stable structures were discovered. The stability, mechanical and electronic structural properties of WSe with three new structures are investigated systematically. For the first time, it is found that WSe undergoes twice phase transitions under different pressures and temperatures. The trigonal P3¯m1 structure is stable at ambient pressure, and it transits to the orthorhombic Pmmn structure at ~33 GPa, then to the cubic Pm3¯m structure at ~105 GPa at 0 K. The coordination number of W increases from 3 to 6, and then to 8. And further the phase diagram of WSe is constructed, which can guide the synthesis of WSe at specific high temperature and pressure. It is helpful to understand the physical properties of transition metal chalcogenides in future.