Integral modeling approach to study the phase behavior of complex solids: application to phase transitions in MgSiO3 pyroxenes.
A combination of electronic structure calculations, classical molecular dynamics simulations and metadynamics is proposed to study the phase behavior of complex crystals. While the former provide accurate energetics for thermodynamic properties, molecular dynamics and metadynamics simulations may reveal new metastable phases and provide insight into mechanisms and kinetics of the respective structural transformations. Here, different simulation methods are used to investigate the polymorphism of MgSiO(3) pyroxenes (enstatites) up to high pressures and temperatures. A number of displacive phase transitions are observed within the three basic structure types clino-, ortho- and protoenstatite using classical molecular dynamics simulations. Transitions between these types require a change of stacking order, which is modeled using a combination of molecular dynamics and metadynamics.