Prediction of the melting curve and phase diagram for CaO using newly developed interatomic potentials

A comprehensive investigation of the melting curve and pressure–temperature (P–T) phase diagram for CaO, a candidate mineral in the Earth's lower mantle, is performed via atomistic simulations applying newly developed interatomic potentials. The efficiency and reliability of the new potentials under high temperature and pressure are verified with lattice dynamics, molecular dynamics, and first–principles approaches, where the fitting values of the potentials are extracted from the lattice parameters, elastic constants, and energy differences of rock–salt (B1) and cesium chloride (B2) phases in CaO. The melting temperatures of CaO with B1 structure at ambient pressure obtained from the single–phase method, void method, and two–phase method are 3080 K, 2775 K, and 2767 K, respectively. The structure and diffusion are evaluated by radial distribution functions, mean square displacements, and self–diffusion coefficients in the solid and liquid states for CaO. Simultaneously, the P–T phase diagram of CaO is calculated up to the core–mantle boundary pressure of 135 GPa, in which the Clausius–Clapeyron relation is introduced to determine the slope of the phase boundary between B1 and B2 phases. Other physical properties, including phase transition pressure, thermal expansion coefficient, isovolumic heat capacity, and entropy, are investigated. The limitations of the new potentials are discussed.