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High-pressure phase transitions in MgSiO₃ orthoenstatite studied by atomistic computer simulation

GeoForschungsZentrum Potsdam, Department 4, Telegrafenberg, 14473 Potsdam, Germany

Correspondence: ^* E-mail: jahn{at}gfz-potsdam.de

Molecular dynamics simulations and first-principles electronic structure calculations are used to study the structural behavior of orthoenstatite, MgSiO₃, at high pressures. The calculations suggest two possible high-pressure polymorphs of orthoenstatite, one with P2₁ca and the other with Pbca symmetry. Both polymorphs are structurally related to orthoenstatite. Molecular dynamics simulations reveal the displacive nature of the phase transitions between the three phases. Electronic structure calculations predict a phase transition from orthoenstatite to the metastable P2₁ca structure at 9 GPa, which may explain the anomalies in elastic and vibrational properties observed experimentally. A second metastable transition from the P2₁ca to the high-pressure Pbca structure may be observable above 20 GPa.

Key Words: DFT • MD simulation • enstatite • phase transition • high pressure