Thermodynamically self-consistent method to predict thermophysical properties of ionic oxides

Abstract

The quasi-harmonic approximation (QHA) model is often used nowadays for prediction of the thermodynamic properties of materials subjected to high pressures and temperatures. However, QHA is not accurate enough in many cases and, as shown in this work, it is not thermodynamically consistent because it leads to violations of the Maxwell relations. The aim of this work is to propose a new thermodynamically self-consistent (TSC) method based on Density Functional Theory (DFT). The proposed method requires minimum information from DFT and no sophisticated equation of state is needed. The TSC method is applied to predicting the thermophysical properties of B1 CaO and K2O up to 2000K and 100GPa. It is shown that the TSC method is consistent with Maxwell relations and is more accurate than the QHA.