Melting temperature prediction by thermoelastic instability: An ab initio modelling, for periclase (MgO)

Melting temperature (TM) is a crucial physical property of solids and plays an important role for the characterization of materials, allowing us to understand their behavior at non-ambient conditions. The present investigation aims i) to provide a physically sound basis to the estimation of TM through a “critical temperature” (TC), which signals the onset of thermodynamic instability due to a change of the isothermal bulk modulus from positive to negative at a given PC-VC-TC point, such that (∂P/∂V)VC,TC = -(∂2F/∂V2) VC,TC = 0; ii) to discuss the case of periclase (MgO), for which accurate melting temperature observations as a function of pressure are available. Using first principles calculations, quasi-harmonic approximation and anharmonic correction, we model the Helmholtz potential, i.e. F(V,T), and determine pressure thereby. A comparison between measured and predicted TM values as a function of pressure shows achievement of an average discrepancy of ~2.9%, in the range 0–25 GPa and 3000–5000 K.