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Phase behavior of protoenstatite at high pressure studied by atomistic simulations

Sandro Jahn^1,* and Roman Martoák²

¹ Deutsches GeoForschungsZentrum (GFZ), Section 3.3, Telegrafenberg, 14473 Potsdam, Germany
² Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynská dolina F2, 84248 Bratislava, Slovakia

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

Structural phase transformations of MgSiO₃ protoenstatite at high pressures are studied by atomic scale simulation techniques. Molecular-dynamics simulations and electronic-structure calculations reveal two metastable polymorphs with space groups P2₁cn and Pbcn, respectively. They are related to protoenstatite by displacive transition mechanisms via subsequent change of the silicate chain rotations from O- to S-type. Metadynamics simulations in combination with molecular dynamics reveal possible mechanisms for the martensitic transition from protoenstatite to high-pressure clinoenstatite. Two different shear mechanisms in the (100) plane are activated during the transition. The first consists of four partial displacements in (100)[001] and (100)[010], whereas in a second step only a single shear in (100)[001] is observed.

Key Words: Molecular dynamics • metadynamics • phase transition • enstatite • MgSiO₃ • protopyroxene • clinopyroxene