Ab initio study of pressure-driven phase transition in FePS3 and FePSe3

In spite of recent findings about the pressure-driven insulator-to-metal phase transition, and emerging superconductivity of FePS3 and FePSe3, the knowledge about their atomic structures is still vague. Here, we investigate the pressure-driven structural phase transitions of FePS3 and FePSe3 from 0 to 35 GPa by using ab initio calculations. We find that the FePS3-C2/m B-I structure transforms to the FePS3-C2/m B-II phase at about 5 GPa. Then above 17 GPa, the FePS3-P (3) over bar 1m B-III phase becomes energetically favored. For FePSe3, with increasing pressure, the FePSe3-R (3) over bar T-I phase transforms to the B-II phase at around 6 GPa and further to the B-III phase at about 15 GPa. Our calculation results are consistent with experimentally observed high-pressure induced cell volume collapse, spin crossovers, and insulator-metal transition in FePS3 and FePSe3, which shed light on understanding the high-pressure physics and phase transitions of FePS3 and FePSe3.