Ab Initio Atomistic Simulations of Ca-Perovskite Melting

Melting curves of Ca-perovskite (pure CaSiO3) were determined by ab initio density functional theory, using two solid-liquid coexistence methods and two free energy approaches, in the form of thermodynamic integration and two-phase thermodynamics. The melting curves based on the solid-liquid coexistence methods and thermodynamic integration rise steeply from 2000 K at 14 GPa to 7000 K at 136 GPa. The melting temperature at 136 GPa is 1400 K higher than previous ab initio predictions. The high thermal stability of Ca-perovskite is linked to its high-symmetry isometric structure and consistent with experiments, demonstrating that Ca-perovskite is the most refractory phase in basaltic compositions in the lower mantle pressure range. The steep dT/dp slope of the melting curve also shows that the Ca-perovskite liquidus field expands relative to those of bridgmanite and silica with increasing pressure, in agreement with experimental evidence from simple and complex systems.