Structural phase transformations and new intermediate phases of MgF2 under high-pressures applied via conjugate-gradient method

Abstract An ab initio constant pressure technique is performed in order to study the structural behavior of MgF 2 under the hydrostatic pressure up to 700 GPa. Two high-pressure phases of MgF 2 are successfully observed through constant pressure simulations. MgF 2 undergoes a phase transformation from the rutile-type structure to the cubic-fluorite-type structure with space group Fm 3 ¯ m at 280 GPa. Another phase transformation from the cubic-fluorite-type structure to the cotunnite-type structure with space group Pnma occurs at 500 GPa. The first transformation proceeds via three intermediate phases with space groups Pnnm , Immm and R 3 ¯ m . We also investigate the stability of these phases from the total energy and enthalpy computations. According to these investigations, the phase transformations should occur from the rutile-type structure to the cubic-fluorite-type structure around 20 GPa and from the cubic-fluorite-type structure to the cotunnite-type structure around 45 GPa.