Temperature and pressure dependent geometry optimization and elastic constant calculations for arbitrary symmetry crystals: Applications to MgSiO₃ perovskites

To optimize lattice parameters for arbitrary symmetry crystals under high temperature and high pressure conditions, a new geometry optimization method for arbitrary symmetry crystals has been proposed in this work. By minimizing non-equilibrium Gibbs energy functions for a series of deformed crystal configurations, the components of deformation tensors have been obtained, and allowing the optimized crystal lattice parameters to be determined. Based on our method and Zhaos method, a new method for calculating high temperature and high pressure elastic constants in arbitrary symmetry crystals has been deduced. To verify the effectiveness of the new method, the high temperature and high pressure lattice parameters and elastic constants of orthorhombic symmetry MgSiO₃ pv have been studied, and a good agreement between calculated and experimental results has been obtained.