High-pressure structural phase transitions and intermediate phases of magnesium fluoride

We investigate the structural behavior of magnesium fluoride (MgF2) under the hydrostatic pressure using constant pressure ab initio technique up to 130 GPa. Through constant pressure simulations, two high-pressure phases of MgF2 are estimated. MgF2 undergoes a phase transformation from the rutile-type structure to the CaCl2-type structure with space group Pnnm at 10-20 GPa. Another phase transformation from the CaCl2-type structure to the α-PbCl2-type structure with space group Pnma occurs at 80-90 GPa. The later transformation is based on three intermediate phases with space groups P21/m, P21 and P212121. These phase transitions are also analyzed from the total energy and enthalpy calculations. These phase changes should occur around 9 and 35 GPa from enthalpy calculations, respectively.